科研之友
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摘要
Above- and below-ground biomass allocation not only reflects plant growth adaptations to environmental variations but also impacts carbon input to the soil and thus terrestrial carbon cycling. In this study, 83 samples were collected from the eastern part of the Qinghai–Tibet Plateau, including 15 species of alpine Rhododendron communities. The aboveground and underground biomass of two different layers of shrub and herb layers were measured using the harvesting method, and we explored the effects of climate factors (such as mean annual temperature, MAT and mean annual precipitation, MAP) on the biomass partitioning pattern. Our results indicated that: (1) The average biomass of the shrub layer was 21.16 t/hm2; above- and below-ground biomass of the shrub layer were 14.90 and 6.26 t/hm2, respectively; the average biomass of the herb layer was 9.79–2.40 t/hm2 above ground and 7.39 t/hm2 below ground, respectively. The root–shoot ratios (R/ S) of the shrub and herb layers were 0.6 and 7.89, respectively, indicating that the shrub layer allocated more biomass to the photosynthetic organs of the above-ground part, and the herb layer allocated more biomass to the roots that absorbed nutrients and water below the ground in the area. (2) After comparing the five major alpine Rhododendron shrubs, significant differences were found in the above- and below-ground biomass in the shrub layer of the different scrubs. The above-ground biomass of the scrubs was in the order Rhododendron adenogynum > R. racemosum > R. capitatum + R. telmateium > R. thymifolium > R. nivale. The below-ground biomass of the scrubs was in the order of R. racemosum > R. adenogynum > R. nivale > R. capitatum + R. telmateium > R. thymifolium. No fundamental difference was found in the above-ground biomass in the herbaceous layer. However, a fundamental difference was observed in the below-ground biomass, and the order of scrub size was as follows: R. nivale > R. capitatum + R. telmateium > R. thymifolium > R. adenogynum > R. racemosum. (3) The above- and below-ground biomass of the shrub layer of Rhododendron alpines in this area followed isometric relations, which was consistent with that of grassland and forest. The shrub layer of R. nivale scrub and herbaceous layer of R. capitatum + R. telmateium scrubs followed allometric relationships, while the other three shrubs indicated isometric relationships in each layer. (4) The biomass of the shrub layer was predominantly influenced by drought, MAT, and MAP. It increased with increase in MAT and MAP, but decreased with increase in drought. The biomass of the herbaceous layer was mainly affected by MAT and MAP and declined with increase in MAT and MAP. The R/S was affected by drought and decreased with increase in MAP. These results indicate that the combination of optimal distribution and allometric growth theories can better explain the allocation and adaptation mechanisms of above- and below-ground biomass in the two layers of the alpine Rhododendron scrubs in the eastern Qinghai–Tibet Plateau.
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