Effects of light availability on leaf attributes and seedling growth of four tree species in tropical dry forest

Background:In tropical dry forests,variation in understory light availability due to season and canopy tree density could be a governing factor in establishment and growth of tree seedlings.Species with varying life history traits are expected to respond differentially to such heterogeneity.We investigated the response of seedlings of four tree species in a tropical day forest in relation to spatiotemporal variability of light.We attempt to explore the role of leaf attributes in explaining intra-and inter-specific variations in relative growth rate.Four study sites,each with three contrasting canopy conditions,were selected along a soil moisture gradient.Seedlings of four tree species(viz.,Acacia catechu,Bridelia retusa,Lagerstroemia parviflora,and Shorea robusta),varying in life history traits,were monitored for seasonal variations in growth traits across canopy condition and sites for 2 years.Results:We observed a larger variation in leaf attributes for pioneer species.A.catechu showed highest mean values for leaf dry matter content,leaf nitrogen concentration,leaf phosphorus concentration,net stomatal conductance,net photosynthetic rate,and relative growth rate in high light conditions.S.robusta and B.retusa demonstrated highest mean values for all the leaf attributes(except leaf dry matter content)in low light conditions.However,intermediate values for leaf attributes were observed in L.parviflora which preferred moderate light conditions.Conclusions:Seasonal variations in light availability at the forest floor appear to play an important role in the establishment and growth of tree seedlings in seasonal dry forests.Leaf attributes can be used to explain intra-and inter-specific variation in response to light availability.Leaf attributes in combinations can be used to predict relative growth rate of tree species in tropical dry environment,which apart from soil moisture is also determined by light availability due to seasonal changes and canopy tree density.

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 con-ditions?and(iv)can the functional attributes in single or in com-bination 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(Amass);mass-based stomatal con-ductance(Gsmass);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 Gsmass,and for RHI,61%variability was due to Amass.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.