Abstract
The above and below–ground biomass (AGB and BGB) relationship is often used to assess the impact of biotic and abiotic effects on the growth and development of individual plants. The AGB and BGB relationship of the same tree species in different habitats can change significantly because of environmental stress. To investigate how the tree size, the biomass allocation and BGB/AGB ratio of Leucaena leucocephala (Lam.) de Wit varied according to spacing and mixed plant patterns in a valley–type savanna of southwest China, we examined the growth of L. leucocephala, and sampled 23 individuals for biomass measurement in each of four treatments (close/wide spacing of Leucaena leucocephala monocultures, mixed plantation of Leucaena leucocephala and Eucalyptus camaldulensis, and mixed plantation of Leucaena leucocephala and Eucalyptus citriodora), and then determined the regression relationships between AGB and BGB of L. leucocephala in different plant stands. Our results indicated that mixed planting significantly reduced all growth metrics for the tree sizes of L. leucocephala and increased the value of BGB/AGB. Changing plant spacing in monocultures had a significant impact on AGB and TB (Total Biomass) of L. leucocephala, but it had no significant effect on the other metrics. Within mixed plant schemes, L. leucocephala significantly reduced the biomass allocation to leaves and small roots and increased the allocation to coarse root biomass. There were no significant differences in tree size and biomass allocation of L. leucocephala between different spacing regimes in monocultures or between different mixtures in mixed plant stands. The correlation between BGB and AGB of L. leucocephala in all plant stands was consistent with the model of allometric growth, and AGB can be used to accurately estimate BGB. Interestingly, the correlations were not exactly the same. BGB and AGB in monoculture showed isometric growth, and their values in mixed plant stands showed allometric growth. BGB also increased faster than AGB. The findings indicated that L. leucocephala allocated more biomass to the root system when it was planted with Eucalyptus.
Highlights
Biomass distribution in plants occurs as a result of environmental adaptation, and it plays a key role in supplying ecosystem services such as those related to primary production, carbon storage, soil conservation, and nutrient cycling [1,2,3,4]
We investigated the effects of plant spacing and mixed planting with non–nitrogen fixing trees (Eucalyptus camaldulensis and E. citriodora) on aboveground biomass (AGB) and belowground biomass (BGB) allocation of L. leucocephala in the valley–type savanna of the Jinsha River
The main objectives of this study are (a) to understand how the biomass allocation and BGB/AGB ratio vary according to spacing and mixed planting patterns and (b) to determine whether the relationships between AGB and BGB of L. leucocephala in different plant stands of the valley–type savanna were consistent with the allometric growth models
Summary
Biomass distribution in plants occurs as a result of environmental adaptation, and it plays a key role in supplying ecosystem services such as those related to primary production, carbon storage, soil conservation, and nutrient cycling [1,2,3,4]. In addition to such practical applications, knowledge about the biomass distribution is essential for understanding basic ecophysiological processes, especially those related to plant life history strategies and tree water balance [5,6]. The biomass distribution favors the stem when photosynthesis is limited, whereas the biomass is favorably distributed to the root when the absorption of mineral elements and water is limited [11,12]
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