Leaf attributes and tree growth in a tropical dry forest

Questions: How are leaf attributes and relative growth rate (RGR) of the dominant tree species of tropical deciduous forest (TDF) affected by seasonal changes in soil moisture content (SMC)? What is the relationship of functional attributes with each other? Can leaf attributes singly or in combination predict the growth rate of tree species of TDF? Location: Sonebhadra district of Uttar Pradesh, India. Methods: Eight leaf attributes, specific leaf area (SLA); leaf carbon concentration (LCC); leaf nitrogen concentration (LNC); leaf phosphorus concentration (LPC); chlorophyll concentration (Chl), mass‐based stomatal conductance (Gs_mass); mass based photosynthetic rate (A_mass); intrinsic water use efficiency (WUEi); and relative growth rate (RGR), of six dominant tree species of a dry tropical forest on four sites were analysed for species, site and season effects over a 2‐year period. Step‐wise multiple regression was performed for predicting RGR from mean values of SMC and leaf attributes. Path analysis was used to determine which leaf attributes influence RGR directly and which indirectly. Results: Species differed significantly in terms of all leaf attributes and RGR. The response of species varied across sites and seasons. The attributes were positively interrelated, except for WUEi, which was negatively related to all other attributes. The positive correlation was strongest between Gs_mass and A_mass and the negative correlation was strongest between Gs_mass and WUEi. Differences in RGR due to site were not significant when soil moisture was controlled, but differences due to season remained significant. The attributes showed plasticity across moisture gradients, which differed among attributes and species. Gs_mass was the most plastic attribute. Among the six species, Terminalia tomentosa exhibited the greatest plasticity in six functional attributes. In the step‐wise multiple regression, A_mass, SLA and Chl among leaf attributes and SMC among environmental factors influenced the RGR of tree species. Path analysis indicated the importance of SLA, LNC, Chl and A_mass in determining RGR. Conclusion: A _mass, SMC, SLA and Chl in combination can be used to predict RGR but could explain only three‐quarters of the variability in RGR, indicating that other traits/factors, not studied here, are also important in modulating growth of tropical trees. RGR of tree species in the dry tropical environment is determined by soil moisture, whereas the response of mature trees of different species is modulated by alterations in key functional attributes such as SLA, LNC and Chl.     

Impact of throughfall deposition and its runoff through different land use surfaces on the chemistry of Ganga water,Varanasi

Limnology - The study was conducted to understand the influence of interactions of atmospheric deposition with different land use surfaces and change in water chemistry of river Ganga through...     

Relative effects of different leaf attributes on sapling growth in tropical dry forest

Aims Soil moisture content (SMC) influences establishment, survival and development of plant species and is considered as the most important limiting factor in tropical dry forest (TDF). In this study we attempt to establish the relationship between leaf attributes and of tree saplings in TDF and address the following questions: (i) how are the functional attributes of dominant tree saplings of TDF affected by seasonal changes in SMC at different habitats?, (ii) what is the relationship of functional attributes with each other?, (iii) how are the functional attributes and their plasticity affected by habitat conditions? and (iv) can the functional attributes in single or in combination predict the growth rate of tree saplings of TDF? The study was conducted on four sites (Hathinala, Gaighat, Harnakachar and Ranitali, listed in order of decreasing SMC) within the tropical dry deciduous forest in northern India.Methods We analysed eight leaf attributes, specific leaf area (SLA); leaf dry matter content (LDMC); leaf nitrogen concentration (leaf N); leaf phosphorus concentration (leaf P); chlorophyll concentration (Chl); mass-based photosynthetic rate (A mass); mass-based stomatal conductance (Gs mass); intrinsic water use efficiency (WUEi) and three growth attributes, relative diameter increment (RDI); relative height increment (RHI); relative growth rate (RGR) of the 10 dominant tree saplings (viz., Acacia catechu, Anogeissus latifolia, Boswellia serrata, Buchanania lanzan, Diospyros melanoxylon, Hardwickia binata, Lagerstroemia parviflora, Lannea coromandelica, Shorea robusta and Terminalia tomentosa) of a TDF and observed the effects of site, season and species for a period of 2 years. Saplings were selected in gradients of deciduousness. Step-wise multiple regression was performed to predict RDI, RHI and RGR from mean values of SMC and leaf attributes.Important findings All the 11 attributes were interrelated and differed significantly among the 10 saplings. Species response varied across sites and seasons. Across the SMC gradient, the attributes showed variable plasticity that differed across species. Among the 10 saplings, the highly deciduous Boswellia serrata showed the maximum plasticity in seven functional attributes. According to the step-wise multiple regressions, 65% variability in RDI and 67% variability in RGR were due to Gs mass, and for RHI, 61% variability was due to A mass. SMC and the other attributes, viz ., SLA, Chl, WUEi and LDMC in combination could contribute only for ~2–6% of the variability in RDI, RHI and RGR, which indicates that other traits/factors, not accounted in this study are also important in modulating the growth of tree saplings in TDFs. In conclusion, growth of the tree saplings in the tropical dry environment is determined by soil moisture, whereas the response of saplings of different tree species is modulated by alterations in key functional attributes such as SLA, Chl, WUEi and LDMC.     

Forest fragmentation and its impact on species diversity: an analysis using remote sensing and GIS

The process of forest fragmentation, a common phenomenon occurring in tropical forests, not only results into continuously forest getting fragmented but also brings about several physical and biological changes in the environment of forests. Consequently, there is a loss of biodiversity due to change in habitat conditions. These remnant fragments provide the last hope for biodiversity conservation. The present study deals with the impact of decreasing patch size of a fragmented forest on the diversity of the tropical dry deciduous forests in Vindhyan highlands, India. There is considerable change in the vegetation cover of this region owing to rapid industrialization and urbanization, which has also contributed to forest fragmentation. In the present study, remotely sensed data has been used to describe the changes brought about in vegetated areas over a period of 10 years as a result of fragmentation and its impact on biodiversity was assessed. Further, in order to assess the loss of species with respect to the reduction in patch size, species area curves for various change areas were analysed. It was observed that the rate of decrease in the number of species is faster in the case of negative change areas as compared to the positive change areas of the region. Various diversity indices also support this observation. Such an analysis would help in formulating appropriate conservation measures for the region.     

Plant functional traits with particular reference to tropical deciduous forests: a review

Functional traits (FTs) integrate the ecological and evolutionary history of a species, and can potentially be used to predict its response as well as its influence on ecosystem functioning. Study of inter-specific variation in the FTs of plants aids in classifying species into plant functional types (PFTs) and provides insights into fundamental patterns and trade-offs in plant form and functioning and the effect of changing species composition on ecosystem functions. Specifically, this paper focuses on those FTs that make a species successful in the dry tropical environment. Following a brief overview, we discuss plant FTs that may be particularly relevant to tropical deciduous forests (TDFs). We consider the traits under the following categories: leaf traits, stem and root traits, reproductive traits, and traits particularly relevant to water availability. We compile quantitative information on functional traits of dry tropical forest species. We also discuss trait-based grouping of plants into PFTs. We recognize that there is incomplete knowledge about many FTs and their effects on TDFs and point out the need for further research on PFTs of TDF species, which can enable prediction of the dynamics of these forests in the face of disturbance and global climate change. Correlations between structural and ecophysiological traits and ecosystem functioning should also be established which could make it possible to generate predictions of changes in ecosystem services from changes in functional composition.     

Foliar demand and resource economy of nutrients in dry tropical forest species

Important phenological activities in seasonally dry tropical forest species occur within the hot‐dry period when soil water is limiting, while the subsequent wet period is utilized for carbon accumulation. Leaf emergence and leaf area expansion in most of these tree species precedes the rainy season when the weather is very dry and hot and the soil cannot support nutrient uptake by the plants. The nutrient requirement for leaf expansion during the dry summer period, however, is substantial in these species. We tested the hypothesis that the nutrients withdrawn from the senescing leaves support the emergence and expansion of leaves in dry tropical woody species to a significant extent. We examined the leaf traits (with parameters such as leaf life span, leaf nutrient content and retranslocation of nutrients during senescence) in eight selected tree species in northern India. The concentrations of N, P and K declined in the senescing foliage while those of Na and Ca increased. Time series observations on foliar nutrients indicated a substantial amount of nutrient resorption before senescence and a ‘tight nutrient budgeting’. The resorbed N‐mass could potentially support 50 to 100% and 46 to 80% of the leaf growth in terms of area and weight, respectively, across the eight species studied. Corresponding values for P were 29 to 100% and 20 to 91%, for K 29 to 100% and 20 to 57%, for Na 3 to 100% and 1 to 54%, and for Ca 0 to 32% and 0 to 30%. The species differed significantly with respect to their efficiency in nutrient resorption. Such interspecific differences in leaf nutrient economy enhance the conservative utilization of soil nutrients by the dry forest community. This reflects an adaptational strategy of the species growing on seasonally dry, nutrient‐poor soils as they tend to depend more or less on efficient internal cycling and, thus, utilize the retranslocated nutrients for the production of new foliage biomass in summer when the availability of soil moisture and nutrients is severely limited.     

Seedling growth of five tropical dry forest tree species in relation to light and nitrogen gradients

Aims Increasing anthropogenic nitrogen (N) deposition has been claimed to induce changes in species composition and community dynamics. A greenhouse experiment was conducted to examine the effect of increased N availability on growth and functional attributes of seedlings of five tree species with different life history characteristics under varying irradiances. The following questions have been addressed: (i) how do the pioneer and non-pioneer species respond in absolute growth and relative growth rate (RGR) to the interaction of light and nitrogen? (ii) how does the interaction between irradiance and nitrogen availability modulate growth attributes (i.e. functional attributes)? (iii) is there any variation in growth responses between leguminous and non-leguminous species along the light and nitrogen gradients?Methods Seedlings of five tree species (Acacia catechu, Bridelia retusa, Dalbergia sissoo, Lagerstroemia parviflora and Terminalia arjuna) were subjected to twelve combinations of irradiance and N levels. Various growth traits, including height (HT), basal area (BA), whole plant dry biomass (M D), leaf mass per unit area (LMA), leaf area ratio (LAR), net assimilation rate (NAR), RGR, biomass fractions, root-to-shoot ratio (R:S) and leaf nitrogen content, were studied to analyse intra- and inter-specific responses to interacting light and N gradients.Important findings Significant interactions for irradiance and N availability for majority of growth attributes indicates that growth and biomass allocation of seedlings were more responsive to N availability under high irradiance. However, species responded differentially to N addition and they did not follow successional status. Slow growers (B. retusa, a shade-tolerant species and L. parviflora, a light demander) exhibited greater response to N enrichment than the fast growers (A. catechu, D. sissoo and T. arjuna). However, N-mediated increment in growth traits was greater in non-legumes (B. retusa, L. parviflora and T. arjuna) compared with that of legumes (A. catechu and D. sissoo). Allocation of biomass to root was strongly suppressed at the highest N supply across species; however, at high irradiance and high N availability, a greater suppression in R:S ratio was observed for B. retusa. NAR was a stronger determinant of RGR relative to LAR, suggesting its prominent role in increased RGR along increasing irradiances. Overall, a higher growth response of slow-growing species to elevated N levels, particularly the non-pioneers (B. retusa and L. parviflora) suggests that future N deposition may lead to perturbations in competition hierarchies and species composition, ultimately affecting community dynamics in nutrient-poor tropical dry forests.