Abstract
Tree allometry plays a crucial role in tree survival, stability, and timber quantity and quality of mixed-species plantations. However, the responses of tree allometry to resource utilisation within the framework of interspecific competition and complementarity remain poorly understood. Taking into consideration strong- and weak-space competition (SC and WC), as well as N2-fixing and non-N2-fixing tree species (FN and nFN), a mixed-species planting trial was conducted for Betula alnoides, a pioneer tree species, which was separately mixed with Acacia melanoxylon (SC+FN), Erythrophleum fordii (WC+FN), Eucalyptus cloeziana (SC+nFN) and Pinus kesiya var. langbianensis (WC+nFN) in southern China. Six years after planting, tree growth, total nitrogen (N) and carbon (C) contents, and the natural abundances of 15N and 13C in the leaves were measured for each species, and the mycorrhizal colonisation rates of B. alnoides were investigated under each treatment. Allometric variations and their relationships with space competition and nutrient-related factors were analyzed. The results showed a consistent effect of space competition on the height-diameter relationship of B. alnoides in mixtures with FN or nFN. The tree height growth of B. alnoides was significantly promoted under high space competition, and growth in diameter at breast height (DBH), tree height and crown size were all expedited in mixtures with FN. The symbiotic relationship between ectomycorrhizal fungi and B. alnoides was significantly influenced by both space competition and N2 fixation by the accompanying tree species, whereas such significant effects were absent for arbuscular mycorrhizal fungi. Furthermore, high space competition significantly decreased the water use efficiency (WUE) of B. alnoides, and its N use efficiency (NUE) was much lower in the FN mixtures. Structural equation modelling further demonstrated that the stem allometry of B. alnoides was affected by its NUE and WUE via changes in its height growth, and crown allometry was influenced by the mycorrhizal symbiotic relationship. Our findings provide new insights into the mechanisms driving tree allometric responses to above- and under-ground resource competition and complementarity in mixed-species plantations, which are instructive for the establishment of mixed-species plantations.
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Claims 10
Claim · model-written summary
Space competition consistently affected the height-diameter relationship of B. alnoides in mixtures with fixing or non-fixing trees.
- Taxon
- B. alnoides
Betula alnoidese0 - Treatment
- space competitione0
- Outcome
- height-diameter relationshipe0
- Qualifier
- in mixtures with FN or nFNe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The results showed a consistent effect of space competition on the height-diameter relationship of B. alnoides in mixtures with FN or nFN.”
Claim · model-written summary
High space competition significantly promoted B. alnoides height growth.
- Taxon
- B. alnoidesBetula alnoidese0
- Treatment
- high space competitione0
- Outcome
- tree height growthe0
- Direction
- promotede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The tree height growth of B. alnoides was significantly promoted under high space competition”
Claim · model-written summary
Mixtures with nitrogen-fixing species expedited B. alnoides DBH, height, and crown size.
- Taxon
- B. alnoidesBetula alnoidese1
- Treatment
- mixtures with FNe0
- Outcome
- growth in diameter at breast height (DBH), tree height and crown sizee0
- Direction
- expeditede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“growth in diameter at breast height (DBH), tree height and crown size were all expedited in mixtures with FN”
e1“height growth of B. alnoides”
Claim · model-written summary
space competition significantly influenced ectomycorrhizal symbiosis of B. alnoides.
- Taxon
- B. alnoidesBetula alnoidese0
- Treatment
- space competitione0
- Interactor
- ectomycorrhizal fungie0symbiont
- Outcome
- symbiotic relationship between ectomycorrhizal fungi and B. alnoidese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The symbiotic relationship between ectomycorrhizal fungi and B. alnoides was significantly influenced by both space competition and N2 fixation by the accompanying tree species”
Claim · model-written summary
N2 fixation by the accompanying tree species significantly influenced ectomycorrhizal symbiosis of B. alnoides.
- Taxon
- B. alnoidesBetula alnoidese0
- Treatment
- N2 fixation by the accompanying tree speciese0
- Interactor
- ectomycorrhizal fungie0symbiont
- Outcome
- symbiotic relationship between ectomycorrhizal fungi and B. alnoidese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The symbiotic relationship between ectomycorrhizal fungi and B. alnoides was significantly influenced by both space competition and N2 fixation by the accompanying tree species”
Claim · model-written summary
Space competition and nitrogen fixation had no significant effects on arbuscular mycorrhizal symbiosis of B. alnoides.
- Taxon
- B. alnoidesBetula alnoidese2
- Treatment
- space competition and N2 fixation by the accompanying tree speciese1
- Interactor
- arbuscular mycorrhizal fungie0symbiont
- Outcome
- arbuscular mycorrhizal fungie0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“such significant effects were absent for arbuscular mycorrhizal fungi”
e1“both space competition and N2 fixation by the accompanying tree species”
e2“mycorrhizal colonisation rates of B. alnoides”
Claim · model-written summary
High space competition significantly decreased B. alnoides water use efficiency.
- Taxon
- B. alnoidesBetula alnoidese0
- Treatment
- high space competitione0
- Outcome
- water use efficiency (WUE)e0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“high space competition significantly decreased the water use efficiency (WUE) of B. alnoides”
Claim · model-written summary
B. alnoides nitrogen use efficiency was much lower in nitrogen-fixing mixtures.
- Taxon
- B. alnoidesBetula alnoidese1
- Treatment
- FN mixturese0
- Outcome
- N use efficiency (NUE)e0
- Direction
- much lowere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“its N use efficiency (NUE) was much lower in the FN mixtures”
e1“height-diameter relationship of B. alnoides”
Claim · model-written summary
The model associated B. alnoides stem allometry with nitrogen and water use efficiency through height growth.
- Taxon
- B. alnoidesBetula alnoidese0
- Outcome
- stem allometrye0
- Qualifier
- via changes in its height growthe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the stem allometry of B. alnoides was affected by its NUE and WUE via changes in its height growth”
Claim · model-written summary
The model associated B. alnoides crown allometry with mycorrhizal symbiosis.
- Taxon
- B. alnoidesBetula alnoidese1
- Outcome
- crown allometrye0
- Qualifier
- mycorrhizal symbiotic relationshipe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“crown allometry was influenced by the mycorrhizal symbiotic relationship”
e1“the stem allometry of B. alnoides”