• P S Ramakrishnan

      Articles written in Proceedings – Plant Sciences

    • Mortal and plastic responses of pure and mixed populations of wheat andChenopodium album L. at two levels of nutrition

      Promila Kapoor P S Ramakrishnan

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      The interference between wheat andChenopodium album was studied in pure and mixed stands at two nutrient levels. Wheat responded to density by plasticity whileC. album responded both by mortality and plasticity. In mixtures, crop had an adverse effect on survival and yield of the weed, though to a lesser degree the effect weed on the crop was also noticed. The ecological aspects of the mortal and plastic responses of the competing species are discussed.

    • Comparative biology of two closely related species ofEuphorbia — Competitive relationships

      P S Ramakrishnan C Kanta

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      The present study reveals a variety of competitive interactions between the two species ofEuphorbia—Euphorbia hirta andEuphorbia thymifolia depending upon the calcium status of the soil. In general,Euphorbia thymifolia suffered high mortality in low calcium soils as compared toEuphorbia hirta. The former, however, showed better survival in high calcium soils. This was more pronounced in mixtures than in pure stands. A similar pattern of behaviour though not so pronounced was also recognised with respect to the growth performance of the two Species in low and high calcium soils. The significance of these results is discussed.

    • On photoblastism in seed germination ofDuabanga sonneratioides Ham.

      R P Shukla P S Ramakrishnan

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      The seeds ofDuabanga sonneratioides Ham. were found to be positively photoblastic and gave fast and maximum germination of 80% in cortinuous light but failed to germinate in the dork. Longer photoperiod favoured germination. Total length of exposure to light rather than the dark period determined the germination of the seeds. Higher temperature favoured germination at a given light exposure treatment. In the field, seeds up to a depth of 2 mm in the soil could germinate. These results have been related to the light demanding nature of this carly suceessional tree species.

    • Reproductive efficiency of secondary successional herbaceous population subsequent to slash and burn of sub-tropical humid forests in north-eastern India

      K G Saxena P S Ramakrishnan

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      Three categories of secondary successional herbaceous communities subsequent ot slash and burn, viz., early successional non-sprouting, early successional sprouting and late successional populations were investigated for their reproductive efficiency considering leaf component since it is the chief organ of photosynthesis. Early successional non-sprouting populations were found to be reproductively the most efficient whereas the early successional sprouting populations allocated more to vegetatively reproducing organs. While the high reproductive potential of early successional non-sprouting species was associated with vigour and production efficiency of the species, this relationship was stronger with the latter characteristic. On the other hand, early successional sprouting populations showed inverse relationship between vegetative and sexual reproductive effort. The strategy of late successional species seems to be to maximize vegetative growth in a closed habitat. The significance of these strategies is discussed in the paper.

    • Structure and function of a sub-tropical humid forest of Meghalaya I. Vegetation, biomass and its nutrients

      Jasbir Singh P S Ramakrishnan

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      The peripheral disturbed zone of a 50-year old stand of the forest at Lailad was dominated byDendrocalamus hamiltonii, an early successional bamboo characteristic of a secondary successional fallow of not more than 20–25 years while the central undisturbed zone hadSchima wallichii, Castanopsis indica andShorea robusta as important components. The biomass of the forest was computed as 137×108 kg/ha of which 64.7% was in the central zone. The contribution by different species both in the central and peripheral zone of the forest was worked out. Linear relationship betweendbh/d2h and biomass was worked out for different species. The standing crop had: N, 953; P, 284; K, 600; Ca, 2281; and Mg, 450 kg/ha, of which 60% was in the central zone of the forest.

    • Structure and function of a sub-tropical humid forest of meghalaya II. Litter dynamics and nutrient cycling

      Jasbir Singh P S Ramakrishnan

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      The litter production in a 50 year old humid sub-tropical forest at Lailad was found to be 5.5 t/ha/yr, 77% of which was through leaf and the remainder through wood. Litter production was more in the peripheral disturbed zone compared to the undisturbed central zone which is related to the successional status of the community. Species differences in the rate of decomposition of litter was noted. Besides litter production and decomposition pattern were related to seasonal differences in temperature and humidity. The present results have been discussed in the light of the data from other studies done elswhere.

    • Structure and function of a sub-tropical humid forest of Meghalaya III. Nutrient flow through water

      Jasbir Singh P S Ramakrishnan

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      This paper deals with water and nutrient flow through incident rainfall, throughfall and stemflow through a 50-year old stand of forest at Lailad. A larger proportion of water was accounted as throughfall and stemflow in March-April and was related to canopy density and this was inversely related to interception loss which was maximum in December. Many of the nutrient concentrations like that of N, K, Ca, etc. increased with the maturation of the leaves during October–November. Though concentration of nutrients was higher in stemflow, the total quantity was morevia throughfall because of larger quantity of water passing through this compartment. More of Ca and K was lost through run-off and percolation due to greater release of these nutrients through litter. The significance of these results have been discussed in the context of secondary succession after slash and burn agriculture (jhum) of which this forms a later stage of community development.

    • Seed germination and seedling establishment of two closely relatedSchima species

      Ram Boojh P S Ramakrishnan

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      Seed germination ofS. khasiana from Upper Shillong andS. wallichii from Shillong, Umsaw and Burnihat in Meghalaya, north-eastern India, and seedling establishment and growth of these species/populations in reciprocal cultivation were studied. Seeds lost viability and germinability gradually within a year when stored at 5 cm below the soil surface under natural conditions or at 20°C in the laboratory. Storage at 0°C permitted retention of 15–25% viability. Seeds germinated better on the surface layers (0–2 cm) of the soil.S. khasiana had a lower temperature optimum (15°C) of germination while the populations ofS. wallichii had a higher temperature optimum (20/25°C). At a temperature of 30°C, the lower altitude population ofS. wallichii from Burnihat gave higher germination than the high altitude population from Shillong. A given species/population ofSchima gave better seedling establishment and growth in its own natural habitat as compared to the introduced populations from the other altitudinal sites. This is indicative of the close adaptation of the natural populations to their habitat and ecotypic differentiation in this species.

    • The science behind rotational bush fallow agriculture system (jhum)

      P S Ramakrishnan

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      Rotational bush fallow agriculture variously termed as shifting agriculture, slash and burn agriculture are commonly known in India asjhum is a traditional agricultural system of the humid tropics and is extensively practised by the tribes of the north-eastern hill region. There is a renewed interest in this agricultural system as it has so much to offer in terms of concepts and ideas to modern agricultural organization. The science behind jhum is based on intuitive experience of the farmer based on long tradition. This paper looks at the science behind jhum with particular emphasis on the ecological and economic significance of mixed cropping, recycling of resources within the system and between jhum and animal husbandry, the non-weed concept weed potential under different cycles of jhum, and nutrient cycling. The distortions brought about by the shortening of the jhum cycle to 4–5 yr is considered. Alternate strategies for development with jhum as the focal point, with suitable modifications but without the present-day distortions, have been considered.

    • Adaptive growth strategy of Khasi pine (Pinus kesiya Royle ex Gordon)

      Ashesh Kumar Das P S Ramakrishnan

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      Three year old open grown pine saplings were selected. Three whorls of shoots were begun in one year. The species thus exhibits a recurrent flushing pattern. Two orders of shoots were recognised on the main leader during the study period of one year. Shoots produced at lower canopy levels attained less extension growth and fewer and shorter needles compared to shoots at higher canopy levels. The growth characteristics of shoots indicated shade intolerant nature of the species. The fascicles of 3 flushes appearing at different times of the year had different patterns of fall and life expectancy. The adaptive strategy of the growth pattern with recurrent flushing and short longevity of the needles are discussed and related to faster growth rate ofPinus kesiya in an early successional environment.

    • Coexistence of closely relatedEupatorium species. I.Eupatorium odoratum L. versusEupatorium adenophorum Spreng. andEupatorium adenophorum Spreng. versusEupatorium riparium Regel. at different altitudes

      Papiya Dev P S Ramakrishnan

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      At their altitudinal limits at 950 m elevation,Eupatorium adenophorum was more susceptible to density-dependent mortality but plasticity of individual organs including reproductive growth was more adversely affected inEupatorium odoratum. In mixtures,Eupatorium adenophorum had an edge overEupatorium odoratum suggesting that the former checks the upper altitudinal limit of the latter.Eupatorium adenophorum andEupatorium riparium coexist well in their mid-altitudinal range of 1500 m. In pure stands,Eupatorium adenophorum was more susceptible to density stress thanEupatorium riparium. Eupatorium riparium was more aggressive thanEupatorium adenophorum in the mixture of increased interspecific competition. In mixtures, these two sets of competing species are less affected than could be expected from the effect of crowding; they, perhaps, occupy different ecologic niches.

    • Coexistence of closely relatedEupatorium species. II.Eupatorium adenophorum Spreng. andEupatorium riparium Regel. at different altitudes

      Papiya Dev P S Ramakrishnan

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      The competitive relationships betweenEupatorium adenophorum andEupatorium riparium were studied at Barapani (950 m) and Upper Shillong (1700 m) using 3 altitudinal populations of the former and one population of the latter.Eupatorium riparium was generally more susceptible to competition from the native population ofEupatorium adenophorum compared to the introduced population. The two species tended to avoid each other in mixtures to a certain degree, due to niche differentiation.

    • Growth and allocation strategy of some important species of seral grasslands at Cherrapunji in north-eastern India

      Subhash C Ram P S Ramakrishnan

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      Growth and allocation patterns of biomass and nutrients of herbaceous species from grasslands at Cherrapunji in north-eastern India were studied under varied nutrient stress situations. Though populations from a nutrient richer soil had better growth rate than those from nutrient poor sites, this difference was not reflected in the tissue concentration of nutrients. Populations in nutrient deficient soils had high allocation to the belowground organs of reproduction than for aboveground parts. ThoughIschaemum andEragrostiella had generally lower nitrogen uptake efficiencies, their use efficiency was fairly high. Soils that are generally nutrient deficient had more C4 grass components than the rich soil underOsbeckia-type.

    • Architectural plasticity of two bamboo species (Nehouzeua dulloa A Camus andDendrocalamus hamiltonii Nees and Arn.) in successional environments in north-east India

      K S Rao P S Ramakrishnan

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      Two bamboo species,Neohouzeua dulloa A Camus andDendrocalamus hamiltonii Nees and Arn. show plasticity in architecture, biomass and nutrient allocation patterns over a successional gradient of up to 60 yr for the former and 25 yr for the latter. However, optimal biomass accumulation rate was attained in a 15 yr old fallow for both species. Maximum elongation and thickness of the zero-order branch (main axis) is attained in a 15 yr old fallow forNeohouzeua dulloa and in a 25 yr old fallow forDendrocalamus hamiltonii. The lower order branches produced on the zero-order branch ofNeohouzeua dulloa are generally sylleptic whereas those ofDendrocalamus hamiltonii are proleptic. Maximum elongation and thickness for the zero-order branch, and least bud dormancy on them occurred in a 15 yr old fallow forNeohouzeua dulloa and in a 25 yr old fallow forDendrocalamus hamiltonii. Dendrocalamus hamiltonii in a 5 yr old fallow had a well developed first-order branch system with diffusely placed lower order branch clusters appearing as if borne on the first-order branch, unlike in older fallows where first-order branch production was continuous and lower order branch clusters appeared as if borne on the zero-order branch itself. In older fallows both species tend to allocate more biomass and nutrients to the below-ground rhizomatous component, as an adaptation for survival and vegetative regeneration after slash and burn disturbance. The growth and architecture of both species are generally geared to capitalize upon the high light regime of the early successional environment, but with a limited ability byNeohouzeua dulloa to tolerate shade.

    • Ecosystem function in a Khasi village of the desertified Cherrapunji area in northeast India

      A K Gangwar P S Ramakrishnan

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      Village ecosystem function of the Khasis in Meghalaya was studied. The land has been desertified around Cherrapunji as the traditional slash and burn agriculture (jhum) has been replaced by plantation systems. Apart from mixed plantations with areca nut, orange, jackfruit, bay leaf, black pepper and betel leaf, broom grass, thatch grass and bamboo are also raised in the village. All the systems generally are economically viable and have a high energy efficiency with labour as the major input. Poultry and swine husbandry are two animal husbandry systems in the village. Both are largely detritus based. About 9% of the produce from mixed areca nut plantation, 50% from the bamboo and entire produce of thatch grass is utilized within the village and the rest is exported. In the absence of agriculture much of the food for consumption is imported from outside the village boundary. The possibility of further useful changes needs evaluation with scientific inputs.

    • Ecological implications of some cash crop ecosystems in north-eastern India

      Anil Kumar P S Ramakrishnan

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      Energy and economic analysis of cash crops (coffee, tea, ginger and pineapple mixed cropping system) are contrasted with shifting agriculture under a 10-yr cycle in north-eastern India. Though ginger gave maximum monetary return, followed by tea, the output/input ratio was higher for pineapple mixed cropping system. Coffee is not successful in this area of study. Some of the cash crop systems had high energy efficiencies though the shifting agriculture had high output/input ratio of 43·5. Nutrient losses through water was high under cash crops with maximal losses under ginger; compared to shifting agriculture the losses were substantial. It is suggested that plantation crops should be sustained in the region basing it, to the extent possible, on the concept of recycling of organic wastes.

    • Growth strategies of early and late successional shrubs from a subtropical moist forest under two light regimes

      U Baruah P S Ramakrishnan

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      Two early successional shrubsMallotus indica Muell. andClerodendron infortunatum Gaertn. and two late successional shrubs,Litsea khasiana Meissn. andCombretum flagrocarpum Herb. were studied under both open and shade environments. The early successional species had greater dry weight allocation to the stem and leaf components and lesser allocation to the root component. Thus the early successional species had an exploitative strategy for effective light capture and utilization of nutrient enriched surface soil after clear-cutting of a forest. On the other hand, the late successional shrubs showed a reverse pattern in allocation. This was related for their survival and to make adequate growth in a competitive environment. These differential strategies of the two categories of shrubs was also reflected in the lower nutrient uptake efficiency and higher use efficiency of the late successional species compared to the early successional ones. Under shade the dry weight production of late successional species was reduced to a less extent than that of early successional species. This would presumably have a competitive advantage for the former category of species.

    • Architecture and growth patterns of early versus late successional shrubs of sub-tropical moist forests of north-eastern India

      U Baruah P S Ramakrishnan

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      Growth and architecture of early versus late successional shrubs are compared and contrasted to evaluate their leaf display characteristics. Early successional shrubs had a higher growth rate over an extended period of time compared to late successional shrubs. Inter-branch length and branch angle were greater for late successional species as compared to early successional ones. First- and second-order branch production over third-order branches was greater in late successional shrubs, whereas the reverse was the case for early successional ones. On the other hand, length contribution by all branch orders was higher for the early successional species. The bifurcation ratio was significantly higher for early successional species growing in the open as compared to late successional shrub species growing in shade. Early successional shrubs follow an exploitive strategy and make faster growth whereas late successionals have a conservative strategy for survival in shade.

    • Leaf dynamics of early versus late successional shrubs of sub-tropical moist forests of north-eastern India

      U Baruah P S Ramakrishnan

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      The two early successional shrubs (Melastoma malabathricum L. andMussenda frondosa L.) are periodic growth leaf-exchanging-types (leaf fall is associated with bud break; leaf span of leaves being approximately 12 months), whereas the two late successional ones (Litsaea khasiana Meissn andOxyspora vagans Wall.) are periodic growth evergreen types (leaf fall is completed well after bud break; life span of leaves being a little over one year). Early successional shrubs have larger leaf production and faster turn-over rates, unlike late successional shrubs with production confined during the early part of the growing season (April–May) is geared to expose larger area over a longer time period, for survival under shade. The early successional shrubs have an exploitative strategy whereas the late successionals are conservative in nature for survival under shade.

    • Cation budget under terrace agroecosystem in Meghalaya in north-east India

      Suprava Patnaik P S Ramakrishnan

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      Cation budgeting was done under 4- and 12-year old terraces at higher elevation of Meghalaya (960 m) in north-east India. Cation addition occurred after burning the biomass arising from the weed and the crop residue prior to cropping. While nutrient removal through weeds was more under 12-year old terrace than under 4-year old one, the reverse was true for that removed by crop. Nutrient deficit, particularly potassium, was obvious under 12-year old terrace. Decline in soil fertility and increase in weed potential are implicated in the reduced crop yield.

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