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Nutrient Uptake and Allocation by Plants in Recent Mounds Created by Subterranean Rodent, Plateau Zokor Eospalax baileyi

Wu R., Wei X., Liu K., Zhong M., Liu Y., Pan D., Shao X.

Polish Journal of Ecology

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2017

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Vol. 65, nr 1

132--143

EN

To understand the nutrient absorption and adaptability of plant species that initially colonize mounds and the influences of the plateau zokor on the diversity of the plant community after 4 years' period, a series of experiments was conducted in an alpine meadow on the Qinghai-Tibetan Plateau. The contents of C and N and the flow of N in pioneer species were measured and tracked using the 15N isotope tracer method, and the species diversity on 4-year-old mounds was investigated. The results showed that (1) plateau zokors could influence the plant species on the mounds by creating gaps in the grassland; (2) Elymus nutans and Elsholtzia feddei, with high rates and efficiencies of nutrient absorption and transportation, were more competitive on the newly formed mounds than other species; (3) Elymus nutans played a dominant role in the plant community of the mounds; and (4) plateau zokors did not change the plant diversity after 4 years' period. These findings indicated that species colonizing the mounds experienced a process of competition when gaps were created by the rodents, that species with greater capabilities for resource acquisition and utilization had stronger competitiveness and vice versa, and that after a few years, the plant diversity on the mounds was almost similar to that of the undisturbed grassland.

2

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

Wang Q., Wu N., Luo P.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

251-260

EN

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.

3

Nutrient resorption and use efficiency at different canopy heights of Alpine tree species Abies georgei var. smithii (Viguie et Gaussen) Cheng, Tibetan Plateau

Li M., Liu D., Kong G.

Polish Journal of Ecology

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2009

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Vol. 57, nr 1

63-72

EN

Nutrients may be mobilized from senescing leaves and transported to other plant tissues, enabling plants to conserve them and reuse. Nitrogen and phosphorus are two dominant nutrients related to photosynthetic capacity and limiting plant growth. In this study, we examined the effect of canopy height on nutrient use by analyzing N and P concentrations of green and senescent leaves collected from different canopy heights of Abies georgei var. smithii (Viguie et Gaussen) Cheng growing at the alpine timberline in Sergyemla Mt.(4 350 m a.s.l), southeastern Tibetan Plateau. The results showed that N and P concentrations per unit needle mass decreased significantly with needle age, but no significant difference was found among upper, middle and lower canopy. However, area-based N and P concentrations increased with the height of canopy. The leaf level nutrient resorption and use efficiency varied in the order: upper canopy> middle canopy >lower canopy for both N and P. The higher nutrient resorption efficiency had significant relationship with leaf level nutrient use efficiency, that is, higher leaf level nutrient use efficiency was partly due to the high resorption from senescent needles. Additionally, the higher nutrient resorption was related to high current nutrient concentration. Vertical variations of leaf level nutrient use efficiency in this study reflected the strategy of alpine trees to respond to imbalance between light availability and soil nutrients.

4

Biomass and nitrogen responses to grazing intensity in an alpine meadow on the eastern Tibetan Plateau

Gao Y.

Polish Journal of Ecology

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2007

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Vol. 55, nr 3

469-479

EN

This study was conducted to examine the seasonal dynamics of biomass and plant nitrogen (N) content under three grazing intensities (light grazing - LG: 1.2, moderate grazing - MG: 2.0, and heavy grazing - HG: 2.9 yaks ha[^-1]) in representative alpine meadow on the eastern Tibetan Plateau. Differentiation in grazing intensity in the study area started since 1997 and has continued to the present time. Plant samples were collected in the middle of June, August and September. The highest aboveground biomass occurred at the MG site for both August and September. Over the growing season, belowground biomass (0.30 cm) increased as grazing intensity increased. The total belowground biomass averaged over all sampling dates was 1226, 1908 and 2244 g m[^-2] for LG site, MG site and HG site, which accounted for 75, 81 and 88% of total biomass, respectively. The results suggested that grazing intensity changed biomass allocation pattern between aboveground and belowground parts of plants. Higher grazing intensity resulted in higher N concentration in both live and dead aboveground biomass over the study period. Increased grazing intensity tended to increase plant N content averaged over all sampling dates, which were 17.9 g m[^-2], 23.8 g m[^-2] and 27.6 g m[^-2] in LG site, MG site and HG site. The results indicated that higher grazing intensity had a potential to increase the ecosystem pool of plant N.