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Biomass Allocation, Compensatory Growth and Internal C/N Balance of Lolium perenne in Response to Defoliation and Light Treatments

Wang L., Wang J., Liu W., Gan Y., Wu Y.

Polish Journal of Ecology

2016

Vol. 64, nr 4

485--499

Light environments can have a considerable influence on how plants respond to defoliation through influencing the biomass allocation patterns and internal C/N ratio. Seedlings of Lolium perenne, a common perennial grass species, were grown for eight weeks under three different light environments (natural light, red light and shading) and two different defoliation treatments (no defoliation versus 50% aboveground biomass removal). This study was conducted to examine (1) the effects of light regimes and defoliation on biomass accumulation, biomass allocation and internal C/N ratio status in plants; (2) how the light regimes influence the pattern of compensatory growth after defoliation; and (3) the relationship between compensatory growth and the internal C/N ratio status. We found that red light altered the shoot-to-root allometry, enhanced the leaf C concentrations and induced N deficiency. By contrast, the leaf N concentrations of L. perenne were greater during shading treatment, which simultaneously enhanced shoot growth and stopped root growth. Under defoliation, red light increased shoot growth, not at the expense of root growth, which was not the same as in natural light and shading treatment. Moreover, regardless of the unclipped (no defoliation) and defoliation conditions, the L. perenne biomass partitioning between roots and shoots was significantly correlated with the leaf N concentrations and C/N ratio, indicating that allometric biomass allocation can be largely modulated by signals related to the C and N status of the plants. These results demonstrated that the leaf C and N status would be an appropriate indicator of compensatory growth after defoliation.

Simulation of light regimes in typical subalpine forest succession series of eastern Tibetan Plateau

Wang Q., Wu N., Luo P.

Polish Journal of Ecology

2009

Vol. 57, nr 2

251-260

Natural regeneration of forest depends on the light regimes of floor. Point-based methods such as fisheye photo and radiometer can not provide a full panorama of light regime of heterogeneous forest stand. Eastern Tibetan Plateau is a major forest belt characteristic of diverse forest type and topographic differentiation. Understanding the trend of changes of light regime along succession series of forest may be helpful for the management of ecosystems. Fragmented forest patches due to tectonic activity and human intervention have made this prediction difficult. We use a spatially explicit forest stand light model (tRAYci) to simulate light distribution within forest in typical subalpine forest succession series of eastern Tibetan Plateau. Due to the spatial heterogeneity of tree distribution in the subalpine area, the forest stand can be approximated with a spatially explicit model of trees. Three typical subalpine forest stands (Sabina forest (SF), Fir forest (FF) and Birch forest (BF)) are selected in the eastern Tibetan Plateau. The dominant species are sabina (Sabina saltuaria (Rehd. et Wils.) Cheng), fir (Abies faxoniana Rehd. et Wils.) and birch (Betula platyphylla Suk.) for each stand and they are spatially clumped in distribution. They represent old growth coniferous forest (SF, 330 years old), coniferous-broadleaved forest (FF, 180 ys) and pioneer broadleaved forest (BF, 40 ys). The parameters of the three-dimensional model of trees are calibrated with field measurements. The simulated values are generally consistent with observed values of radiation measured by radiometers installed in these stands and values derived from fisheye photos. Test failures may be caused by the incomplete submodel of crown as a gap free one. Light regimes in old growth and pioneer forest are much more heterogeneous than intermediate stages of forest. Light regimes of these forests are also reflected by the composition of understory herb layers.