Abstract
BACKGROUND AND AIMS: The mobile carbon supply to different compartments of a tree is affected by climate, but its impact on cell-wall chemistry and mechanics remains unknown. To understand better the variability in root growth and biomechanics in mountain forests subjected to substrate mass movement, we investigated root chemical and mechanical properties of mature Abies georgei var. smithii (Smith fir) growing at different elevations on the Tibet-Qinghai Plateau. METHODS: Thin and fine roots (0·1-4·0 mm in diameter) were sampled at three different elevations (3480, 3900 and 4330 m, the last corresponding to the treeline). Tensile resistance of roots of different diameter classes was measured along with holocellulose and non-structural carbon (NSC) content. KEY RESULTS: The mean force necessary to break roots in tension decreased significantly with increasing altitude and was attributed to a decrease in holocellulose content. Holocellulose was significantly lower in roots at the treeline (29·5 ± 1·3 %) compared with those at 3480 m (39·1 ± 1·0 %). Roots also differed significantly in NSC, with 35·6 ± 4·1 mg g(-1) dry mass of mean total soluble sugars in roots at 3480 m and 18·8 ± 2·1 mg g(-1) dry mass in roots at the treeline. CONCLUSIONS: Root mechanical resistance, holocellulose and NSC content all decreased with increasing altitude. Holocellulose is made up principally of cellulose, the biosynthesis of which depends largely on NSC supply. Plants synthesize cellulose when conditions are optimal and NSC is not limiting. Thus, cellulose synthesis in the thin and fine roots measured in our study is probably not a priority in mature trees growing at very high altitudes, where climatic factors will be limiting for growth. Root NSC stocks at the treeline may be depleted through over-demand for carbon supply due to increased fine root production or winter root growth.
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Claims 4
Claim · model-written summary
Root tensile force needed to break roots of Abies georgei decreased significantly with increasing altitude.
- Taxon
- Abies georgei
.jpg?width=60)
Abies georgeie0 - Organ / stage
- rootse1
- Outcome
- mean force necessary to break roots in tensione1
- Direction
- decreasede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“Abies georgei var. smithii”
e1“The mean force necessary to break roots in tension decreased significantly with increasing altitude”
Claim · model-written summary
Holocellulose content was significantly lower in roots at the treeline than at 3480 m elevation.
- Taxon
- Abies georgeiAbies georgeie0
- Organ / stage
- rootse2
- Outcome
- Holocellulosee2
- Direction
- lowere2
- Value
- 29·5 ± 1·3 %e2
- Qualifier
- 39·1 ± 1·0 %e2
- Comparator
- 3480 me2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Abies georgei var. smithii”
e2“Holocellulose was significantly lower in roots at the treeline (29·5 ± 1·3 %) compared with those at 3480 m (39·1 ± 1·0 %)”
Claim · model-written summary
Non-structural carbohydrate (NSC) content of roots was lower at the treeline than at 3480 m.
- Taxon
- Abies georgeiAbies georgeie0
- Organ / stage
- rootse3
- Outcome
- NSCe3
- Direction
- lowerinferrede3
- Value
- 18·8 ± 2·1 mg g(-1) dry masse3
- Qualifier
- 35·6 ± 4·1 mg g(-1) dry masse3
- Comparator
- 3480 me3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Abies georgei var. smithii”
e3“Roots also differed significantly in NSC, with 35·6 ± 4·1 mg g(-1) dry mass of mean total soluble sugars in roots at 3480 m and 18·8 ± 2·1 mg g(-1) dry mass in roots at the treeline”
Claim · model-written summary
The decrease in root tensile force with altitude is attributed to a decrease in holocellulose content.
- Taxon
- Abies georgeiAbies georgeie0
- Organ / stage
- rootse4
- Compound
- holocellulosee4
- Outcome
- mean force necessary to break roots in tensione4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Abies georgei var. smithii”
e4“The mean force necessary to break roots in tension decreased significantly with increasing altitude and was attributed to a decrease in holocellulose content”