Seedling light limitation does not increase across a natural productivity gradient

Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plant community structure,has been tested many times in artificial productivity gradients(fertilization studies),but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient,I conducted a cross-site field experi-ment in southwest michigan,USA.A each of six old fields natu-rally varying in productivity,I exposed transplanted seedlings of big bluestem(Andropogon gerardii)to a light addition(tie-back)treat-ment that increased light availability and measured their biomass after one and two growing seasons.Important Findingsseedlings responded positively to the tie-back treatment,but positive responses did not increase across the natural productivity gradient.These results suggest that although light does limit seedling establishment,the strength of light limitation does not depend on variation in productivity in natural systems.Instead,light limitation interacted with a variety of site differences to determine establishment.although the general principle that light limitation increases with productivity is well established,these results indicate that it may not always occur in natural systems.

A simple data assimilation method for improving the MODIS LAI time-series data products based on the object analysis and gradient inverse weighted filter

A simple data assimilation method for improving estimation of moderate resolution imaging spectroradiometer （MODIS） leaf area index （LAI） time-series data products based on the gradient inverse weighted filter and object analysis is proposed. The properties and quality control （QC） of MODIS LAI data products are introduced. Also, the gradient inverse weighted filter and object analysis are analyzed. An experiment based on the simple data assimilation method is performed using MODIS LAI data sets from 2000 to 2005 of Guizhou Province in China.