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Nitrogen content and biomass : scaling from the tree to the forest level

Cheng D.-L., Zhong Q.-L.

Polish Journal of Ecology

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2012

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Vol. 60, nr 4

699--706

EN

Nitrogen is an essential nutrient for plant growth. Although much has been learned about its utilization and distribution within the plant body, little is known about the relationship between nitrogen content and standing biomass at the level of entire forests. Data for nitrogen content (N) and biomass (M) of 10 deciduous species in USA at the individual trees level and 37 species grown in three forest biomes (i.e. tropic, subtropics, and temperate) in China at stands level were gathered to determine the N versus M scaling relationships for different tissue- and organ-types (e.g. bark and leaves). Model Type II regression protocols were used to calculate scaling exponents and allometric constants (i.e. slopes and y-intercepts of log-log bivariate plots, respectively) between N and M to. At the level of individual plants, N scaled nearly isometrically with M for the different tissue- and organ-types (i.e. N [proportionality] M [0.97–1.04]). At the stand-level, N scaled similarly with respect to leaf, branch, and bark M, despite differences in stand size-frequency distributions and species composition. However, total stand N scaled allometrically with respect to total stem or root M and thus to total stand mass (i.e. N [proportionality] M[T] [0.77–0.87]). This was attributed to the accumulation of wood (and other ‘necromass’ tissue components that have lower N content than physiologically active tissues) in progressively older (and thus more massive) tree stands. When coupled to the scaling of N with respect to annual plant growth rates, these exponents provide important boundary conditions with which to model forest nutrient cycling.

2

Life history strategy influences biomass allocation in response to limiting nutrients and water in an arid system

Mao W., Allington G., Li Y., Zhang T., Zhao X., Wang S.

Polish Journal of Ecology

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2012

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Vol. 60, nr 3

545-557

EN

The optimal partitioning theory (OPT) predicts that a plant should allocate relatively more biomass to the organs that acquire the most limiting resource. However, variation in biomass allocation among plant parts can also occur as a plant grows in size. As an alternative approach, allometric biomass partitioning theory (APT) asserts that plants should trade off their biomass between roots, stems and leaves, and this approach can minimize bias when comparing biomass allocation patterns by accounting for plant size in the analysis. We analyzed the biomass allocation strategy of the two species: annual Setaria viridis (L.) Beauv and perennial Pennisetum centrasiaticum Tzvel from the Horqin Sandy Land of northern China by treating them with different availabilities of soil nutrient and water (added in summer and winter), and hypothesized that the two species have different patterns of biomass allocation strategy in response to different soil water content and soil nitrogen content. After taking plant size into account, the biomass allocation strategy of S. viridis and P. centrasiaticum differed in response to nitrogen and water; leaves and root:shoot ratio (RTS) of S. viridis were "true" in response to various soil nitrogen contents. The plasticity of roots was also "true" in response to fluctuation in soil water content. However, P. centrasiaticum showed a different pattern with no shift of biomass allocation strategy in response to nitrogen and water. Adjustment in organs biomass allocation pattern of S. viridis in response to nitrogen and water limitation was dramatic, this suggested that S. viridis support optimal partitioning theory (OPT). P. centrasiaticum has better tolerance to varied environments and more likely support the allometric biomass partitioning theory (APT), this characteristic may allow P. centrasiaticum to keep dominance in fragile habitats.

3

Invariant allometric relationship between aboveand below-ground biomass along a moisture gradient in North-West China

Cheng D., Wang G., Tang Q., Li T., Zhong Q.

Polish Journal of Ecology

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2009

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Vol. 57, nr 4

669-675

EN

Biomass allocation pattern is an important plant characteristic which influences how plants respond to abiotic and biotic heterogeneity. Prior studies indicate that above-ground biomass scales nearly isometrically with respect to below-ground biomass regardless of environment or phyletic affinity. However, such rule has been mostly tested with data on trees and usually without drought stress. Given the importance of this predicted relationship, it should be evaluated for a wider range of species and environmental conditions. Variations of the above- and belowground biomass (M[A] and M[R], respectively) were determined from five sites in north-west China, which compose a natural moisture gradient (aridity index ranging from 0.95 to 1.98). Model Type II regression protocols were used to compare the numerical values of M[A] vs M[R] scaling exponents (i.e. slopes of log-log linear relationships). The resulting five scaling exponents were indistinguishable and had a similar, nearly isometric slope (i.e. M[A] [is proportional to] M[R] [is approximately equal to] 1.0). Significant variation was observed in the Y-intercepts of the five regression curves, because of the absolute differences in M[A] or M[R]. These results support prior allometric theory, which reveals an isometric relationship between above- and below-ground biomass, and may provide a suitable method to estimate the regional below-ground biomass based on the direct aboveground measurements.

4

Effect of genetic relatedness on the allometric relationship between biomass investment and sexual reproduction in clonal plant

Stojković B., Barisic Klisaric N., Avramov S., Tarasjev A.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

371-375

EN

In order to analyze changes in biomass allocation patterns across genetically structured populations where plants are competing for access to light, we performed glasshouse experiment with controlled genetic identity of competitors. Clonal replicates of 17 Lamium maculatum (L.) genotypes were grown in three treatments: control (low competition for light availability), intraclonal and interclonal competition. It was shown that competition between genetically unrelated individuals (interclonal treatment) was the most stressful environment for Spotted Dead Nettle. Results of allometry analyses, based on standardized major axis (SMA) mathematical procedure, have shown the smallest differences in relative investment to sexual reproduction between larger and smaller individuals when competing with unrelated plants. Our results indicate that allometric relationships between vegetative and reproductive traits could be strongly affected by genetic relatedness of competing plants.