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Variations in biomass, production, and respiration of fine roots in a young larch forest
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| Title: | Variations in biomass, production, and respiration of fine roots in a young larch forest |
| Other Titles: | カラマツ若齢林における細根のバイオマス，生産量および呼吸の変動 |
| Authors: | 崔, 鋭 Browse this author |
| Issue Date: | 24-Mar-2022 |
| Publisher: | Hokkaido University |
| Abstract: | Soil respiration (Rs) accounts for 30–80% of total respiration in forest ecosystems, indicating Rs plays a crucial role in terrestrial carbon cycles. The Rs is composed of root respiration (Rr) and microbial heterotrophic respiration (Rh). Plant roots are different in metabolism and functions according to size and order. Fine roots (typically < 2 mm in diameter) perform important functions and govern belowground carbon cycles. However, the phenological variation of the functions is not well understood. Thus, we adopted an approach to partition Rr into respirations for growth (Rg), maintenance (Rm), and ion uptake (Rion) using modified empirical models. We conducted field experiments on Rs and fine root dynamics, and transpiration in a larch-dominated young forest on the bare ground after removing surface organic soil to parameterize the models. The field experiments were conducted in 2017–2018 (E1) and 2019–2020 (E2) in a regenerating forest dominated by Japanese larch in Tomakomai, Hokkaido. The top organic soil was removed after typhoon disturbance in 2004. Collar pairs consisting of control (CC) and trenched (TC) ones were installed at 0.5 m (N) and 1 m (F) from isolated larch trees (n = 10 (E1) and 18 (E2)). Soil CO2 fluxes (RCC and RTC) were periodically measured on the collars by a chamber method. The RCC and RTC were continuously estimated throughout the experimental periods from soil temperature (Ts) using exponential equations. CO2 efflux through dead root decomposition (RDR) in trenched collars was also estimated. The Rh was calculated as RTC – RDR, and Rr was derived as RCC – Rh. Fine root biomass (Bf, g DM m-2) and production (Pf, g DM m-2 d-1) were periodically measured in CC by the sequential coring and ingrowth core methods, respectively. In addition, sap flow was measured by a thermal dispersion method only in E2. The following two models were applied to partition Rr (g C m-2 d-1):
𝑅r = 𝑅m + 𝑅g = 𝑐1 ∙ 𝑃f + 𝑑1 ∙ 𝑒𝑥𝑝(𝑓1 ∙ 𝑇s) ∙ (𝐵f + 𝐵c) (1)
𝑅r = 𝑅m + 𝑅g + 𝑅ion = 𝑐2 ∙ 𝑃f + 𝑑2 ∙ 𝑒𝑥𝑝(𝑓2 ∙ 𝑇s) ∙ (𝐵f + 𝐵c) + 𝑔 ∙ 𝑇r ∙ 𝐵f (2)
where c, d, f, and g are fitting parameters, Bc coarse root biomass (g DM m-2), and Tr transpiration per fine root biomass (g H2O g DM-1 d-1). Annual Rs was 493 ± 45 (N) and 311 ± 34 g C m-2 yr-1 (F) (mean ± standard error) in E1, and Rr accounted for 37% (N) and 16% (F) of Rs. Despite no seasonal variation in Bf, Pf decreased in the cold season. Annual Pf was 81 ± 22 (N) and 41 ± 10 g DM m-2 yr-1 (F), and ii annual mean Bf was 70 ± 9 (N) and 13 ± 3 g DM m-2 yr-1 (F). Model 1 (M1) was significantly parameterized (r2 = 0.59, p < 0.001) using the field data (n = 50). Annual Rr was estimated to be 107 g C m-2 yr-1 and accounted for 25% of Rs. The Rr was partitioned into fine root Rg, fine root Rm, and coarse root Rm by 30, 44 and 26%, respectively. In E2, annual Rs was 610 ± 26 (N) and 474 ± 52 g C m-2 yr-1 (F), and Rr accounted for 47% and 45% of Rs, respectively. The Bf increased slightly in the growing season, whereas Pf clearly decreased in the cold season and peaked in July. Annual Pf was 115 ± 7 (N) and 102 ± 10 g DM m-2 yr-1 (F), and mean Bf was 133 ± 13 (N) and 78 ± 14 g DM m-2 yr-1 (F). The Bc was less than a third of Bf. Models 1 and 2 were significantly parameterized (r2 = 0.51–0.53, p < 0.001) using the field data (n = 144). Although the parameters of d (Rm at 0°) and f (the temperature coefficient of Rm) were almost the same between the two models, the parameter of Rg (c) was smaller for M1. The Rm and Rion peaked in June–July, whereas Rg peaked earlier in June. Annual Rr was estimated to be 215 g C m-2 yr-1 and accounted for 41% of Rs. The Rr was partitioned into fine root Rg, fine root Rm, coarse root Rm, and fine root Rion by 32, 46, 13 and 9%, respectively. The two models were significantly fitted to field data. Although all parameters in M1 were significant determined in both experiments, those from E2 would be more robust because of more data sets for curve fitting and the addition of spatial distribution of coarse root biomass. The parameters of d and f related to Rm were almost the same between M1 and M2 in E2; the Q10 of Rm calculated from parameter f was 2.46–2.61. However, the parameter of c for Rg was lower by 20% in M2, suggesting that Rion was assigned to Rg in M1, because Rion was reported to be proportional to Rg from laboratory experiments. Using M2, we estimated that fine roots account for 87% of total Rr annually, and fine root Rr was partitioned into Rg, Rm, and Rion by 37, 53, and 10%, respectively. The Rg, Rm, and Rion varied according to the seasonal variations of Pf, Ts, and Tr, respectively. To partition Rr into Rg, Rm, and Rion, we applied modified empirical models and parameterized them using seasonal field data of soil CO2 efflux, Bf, Pf, Bc, Ts, and Tr measured in a young larch-dominated forest regrowing after the removal of surface organic soil. In such a simplified filed condition, we succeeded in significant partitioning of root respiration in a filed condition. Despite ignoring coarse root growth, the results suggest that our approach is capable of partitioning root respiration. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第14823号 |
| Degree Level: | 博士 |
| Degree Discipline: | 農学 |
| Examination Committee Members: | (主査) 教授 平野 高司, 教授 鮫島 良次, 准教授 加藤 知道 （食資源） |
| Degree Affiliation: | 農学院（農学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/88855 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 農学院(Graduate School of Agriculture)
学位論文 (Theses) > 博士 （農学）
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