Effects of previous nitrogen addition on aboveground and belowground carbon and nitrogen allocation dynamics in drought-exposed sessile oak seedlings

doi:10.17521/cjpe.2024.0218

Abstract

Abstract:

Aims Drought effects on the carbon (C) balance are considered the major factor of tree mortality and are assumed to be regulated by soil nutrient (e.g., nitrogen (N)) availability. However, the effects of nitrogen addition on trees’ carbon and nitrogen distribution between aboveground and belowground and the coupling between carbon and nitrogen relations in various organs in response to drought are still unclear in trees.
Methods A two-year full factorial microcosm experiment was set up with sessile oak (Quercus petraea). Nitrogen addition was performed in the first year, and a drought treatment was conducted in the second year. Isotope ¹⁵N and ¹³C labelling were carried out before drought and during drought, respectively. Three consecutive samplings were conducted after the dual labelling with ¹³C and ¹⁵N in the second year, and the effects of nitrogen addition on carbon and nitrogen allocation dynamics during progressive drought were tested.
Important findings Our results showed that previous nitrogen addition promoted photosynthetic carbon fixation and nitrogen allocation, increased root nitrogen uptake, reduced the non-structural carbohydrates (NSC) contents in all organs and changed the relationships of carbon and nitrogen in aboveground and belowground organs. In contrast, drought had minor effects on nitrogen and carbon allocation between aboveground and belowground and the relationship of carbon with nitrogen in all organs (represented by the ratio of ¹³C to ¹⁵N in all organs). Drought only significantly reduced the content of NSC. During drought (from day 40 to 73), previous nitrogen addition led sessile oak to prioritise belowground carbon and nitrogen allocation. Our results indicate that sessile oak can change its carbon and nitrogen allocation strategies to adapt to drought, while previous nitrogen addition may increase its drought sensitivity.

Key words: nitrogen addition, drought, carbon allocation, nitrogen allocation, ¹³C isotope labelling, ¹⁵N isotope labelling

FENG Mei, OUYANG Sheng-Nan, Matthias SAURER, LI Mai-He, ZHOU Xiao-Qian, TIE Lie-Hua, SHEN Wei-Jun, DUAN Hong-Lang, Arthur GESSLER. Effects of previous nitrogen addition on aboveground and belowground carbon and nitrogen allocation dynamics in drought-exposed sessile oak seedlings[J]. Chin J Plant Ecol, 2025, 49(9): 1527-1542.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0218

https://www.plant-ecology.com/EN/Y2025/V49/I9/1527

Figures/Tables 10

Fig. 1 Dynamics of net photosynthesis and predawn leaf water potential in sessile oak under nitrogen (N) addition and drought (mean ± SE, n = 3). N0, no N addition treatment; N+, N addition treatment. Different lowercase letters indicate significant differences among the different processing time (p < 0.05).

Table 1 Effects of nitrogen addition, drought, sampling time, and their interaction on the ratio of 13C and 15N content in all orangs, net photosynthetic rate, and predawn leaf water potential of sessile oak (p value)

因素 Factor	¹³C:¹⁵N				净光合速率 Net photosynthetic rate (µmol·m^-2·s^-1)	叶片凌晨水势 Predawn leaf water potential (MPa)
因素 Factor	叶 Leaf	茎 Stem	细根 Fine root	粗根 Coarse root	净光合速率 Net photosynthetic rate (µmol·m^-2·s^-1)	叶片凌晨水势 Predawn leaf water potential (MPa)
N	0.009	0.008	<0.001	<0.001	0.136	0.732
D	0.993	0.850	0.199	0.853	<0.001	<0.001
Time	0.302	0.356	0.011	0.002	<0.001	0.004
D × Time	0.867	0.796	0.167	0.692	0.116	0.027
N × Time	0.310	0.273	0.139	0.015	<0.001	0.193
D × N	0.888	0.917	0.931	0.655	0.901	0.767
D × N × Time	0.854	0.719	0.210	0.773	0.240	0.049

Fig. 2 Relative 13C allocation to different organs in sessile oak under nitrogen (N) addition and drought at three harvest times (mean ± SE, n = 3). N0, no N addition; N+, N addition treatment. Different uppercase letters indicate significant differences between the no N addition and the N addition treatment (p < 0.05), and different lowercase letters indicate significant differences among the three sampling time points (the 15, 40 and 73 days after rewetting) (p < 0.05).

Table 2 Effects of nitrogen addition, drought, sampling time, and their interaction on the relative allocation ratio of 15N, 13C, and the ratio of aboveground to belowground allocation in sessile oak organs (p value)

因素 Factor	叶相对分配比例 Leaf relative allocation ratio		茎相对分配比例 Stem relative allocation ratio		细根相对分配比例 Fine root relative allocation ratio
因素 Factor	¹³C	¹⁵N	¹³C	¹⁵N	¹³C	¹⁵N	¹³C	¹⁵N	¹³C	¹⁵N
N	0.948	0.124	0.025	0.159	0.027	0.001	0.154	0.736	0.003	0.039
D	0.760	0.505	0.756	0.263	0.978	0.283	0.590	0.758	0.188	0.072
Time	0.974	0.251	0.187	0.450	0.017	0.089	0.722	0.588	0.063	0.015
D × Time	0.942	0.878	0.890	0.413	0.461	0.148	0.523	0.967	0.039	0.038
N × Time	0.549	0.609	0.352	0.127	0.191	0.319	0.255	0.911	0.003	<0.001
D × N	0.082	0.020	0.838	0.127	0.657	0.764	0.321	0.618	0.151	0.432
D × N × Time	0.191	0.036	0.905	0.508	0.707	0.347	0.730	0.260	0.594	<0.001

Fig. 3 Relative allocation ratio of 15N in organs of sessile oak under nitrogen (N) addition and drought at three harvest times (mean ± SE, n = 3). N0, no N addition; N+, N addition treatment. Different uppercase letters indicate significant differences between the no N addition and the N addition treatment (p < 0.05), and different lowercase letters indicate significant differences among the three time pointsof sampling (p < 0.05).

Table 3 Effects of nitrogen addition, drought, sampling time, and their interaction on non-structural carbohydrates (NSC) content and root nitrogen uptake rate in various organs of sessile oak (p value)

因素 Factor	叶NSC含量 Leaf NSC content (%)	茎NSC含量 Stem NSC content (%)	细根NSC含量 Fine root NSC content (%)	粗根NSC含量 Coarse root NSC content (%)	根系氮吸收速率 Root nitrogen uptake rate (%)
N	0.016	0.004	0.032	0.261	<0.001
D	0.344	0.153	0.030	<0.001	0.136
Time	0.008	0.003	0.228	<0.001	<0.001
D × Time	0.563	0.250	0.022	<0.001	0.116
N × Time	0.205	0.929	0.726	0.072	<0.001
D × N	0.797	0.096	0.842	0.351	0.901
D × N × Time	0.863	0.103	0.684	0.700	0.240

Fig. 4 Tissues’ non-structural carbohydrate content in sessile oak under nitrogen (N) addition and drought at three harvest times (the 15, 40 and 73 days after rewetting) (mean ± SE, n = 3). N0, no N addition; N+, N addition treatment. Different lowercase letters indicate significant differences among the three sampling time points (p < 0.05); * indicate significant differences between the no N addition and the N addition treatment under the two watering regimes (p < 0.05).

Fig. 5 Root nitrogen uptake rate in sessile oak under nitrogen (N) additions and drought at three harvest times (mean ± SE, n = 3). DN+, drought-exposed sessile oak with N addition; DN0, the drought-exposed sessile oak without N addition; WN+, the well-watered sessile oak with N addition; WN0, the well-watered sessile oak without N addition. Different uppercase letters indicate significant differences between the no N addition and the N addition treatment (p < 0.05), and different lowercase letters indicate significant differences among the three time points of sampling (p < 0.05).

Fig. 6 Rate of 13C to 15N content in sessile oak under nitrogen (N) additions and drought at three harvest times (mean ± SE, n = 3). N0, no N addition; N+, N addition treatment. Different lowercase letters indicate significant differences among the three sampling time points (p < 0.05), * indicate significant differences between the no N addition and the N addition treatment under the two watering regimes (p < 0.05).

Fig. 7 Effects of previous nitrogen addition, drought, and their combination on the coupling relationship between aboveground and underground carbon (C) and nitrogen (N) in sessile oak. represent no significant effects, inhibition and promotion, respectively. Grey arrows indicate nitrogen transport from belowground to aboveground, white arrows indicate photosynthetic carbon transport from aboveground to belowground, and the closed loop in the middle indicates that photosynthetic carbon synthesis and distribution in the aboveground part and nitrogen absorption and distribution in the belowground root system form a coupled process.

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