不同遮荫处理对杉木幼苗生长及土壤碳氮代谢酶活性的影响

遮荫是苗木培育的关键措施,它可以通过影响根系向土壤释放分泌物的量改变土壤碳氮酶活性,进而影响土壤碳氮循环过程。然而,有关遮荫对土壤碳氮酶活性的影响及其与苗木生长之间的关系如何,研究较为缺乏。以杉木1年生幼苗 "洋061"为研究对象,设置五个不同遮荫处理:不遮荫(CK)光强1157.82 μmol m^-2 s^-1、30%遮荫(T1)光强856.31 μmol m^-2 s^-1、55%遮荫(T2)光强542.68 μmol m^-2 s^-1、70%遮荫(T3)光强382.08 μmol m^-2 s^-1、85%遮荫(T4)光强219.56 μmol m^-2 s^-1,比较不同遮荫处理对杉木幼苗生长、土壤有机碳(SOC)、全氮(TN)含量和土壤碳氮代谢酶活性的影响。结果表明:(1)杉木苗高、不同器官生物量、根冠比和苗木质量指数均随光强减弱呈先升后降的趋势,除苗高和根冠比分别在T3和T1时最大,其余指标均在T2时最大,而地径则随光强的减弱逐渐变小;(2)土壤SOC含量对遮荫响应存在差异,T3处理下SOC含量显著低于CK,而在T4时显著高于CK,遮荫不同程度降低土壤TN含量,但不同处理间不存在显著差异;(3)土壤碳氮代谢酶对不同遮荫处理的响应存在一定的差异。与CK相比,不同遮荫处理显著改变土壤酶活性,其中土壤纤维素酶(S-CL)、土壤蔗糖酶(S-SC)、土壤酸性转化酶(S-AI)、土壤木质素过氧化物酶(S-LiP)活性在T4处理时最高;土壤过氧化氢酶(S-CAT)、土壤β-N-乙酰氨基葡萄糖苷酶(S-NAG)、土壤几丁质酶(S-C)则在T3达到最大值;土壤多酚氧化酶(S-PPO)活性在T1处理下最大;T2遮荫强度时,土壤淀粉酶(S-AL)、土壤亚硝酸转化酶(S-NiR)活性最高;但遮荫还不同程度的降低了土壤脲酶(S-UE)、土壤硝酸转化酶(S-NR)活性。冗余分析发现,土壤酶活性对SOC、TN的解释度高达76.61%,表明S-LiP、S-AL、S-AI、S-PPO、S-CL与SOC具有较强的正相关关系,S-UE、S-NR对TN影响较大。综上所述,30%-55%遮荫即光照强度为542.68-856.31 μmol m^-2 s^-1是较适宜杉木幼苗生长的光照条件,这与该处理下提高土壤碳氮酶活性进而改善碳氮养分循环密切相关。

Effects of shading on the growth and soil carbon, nitrogen metabolism enzyme activities of Cunninghamia lanceolata seedlings

Shading is a key measure in seedling cultivation, which can change the soil carbon and nitrogen enzyme activity by affecting the release of root exudates to soil, and in turn affect the key processes of soil carbon, nitrogen cycle. However, the effect of shading on soil carbon and nitrogen enzyme activity and its relationship with seedling growth remains unclear. A pot experiments with five different light intensities (No shading (CK: 1157.82 μmol m^-2 s^-1)、30% Shading (T1: 856.31 μmol m^-2 s^-1)、55% shading (T2: 542.68 μmol m^-2 s^-1)、70% shading (T3: 382.08 μmol m^-2 s^-1)、85% shading (T4: 219.56 μmol m^-2 s^-1) were conducted by using one-year-old superior clone of Cunninghamia lanceolata ''Yang061’ seedlings to investigate the effects of shading treatments on the growth of C. lanceolata seedlings, soil organic carbon (SOC), total nitrogen (TN) content and soil carbon, nitrogen metabolism enzyme activity. The results showed that: (1) The seedling height, different organ biomass, root-shoot ratio and seedling quality index of C. lanceolata displayed first increased then decreased tendency with the decrease of light intensities. Moreover, we also found that most indexes mentioned above achieved their maximum at T2 treatment except for seedling height and root-shoot ratio which reached their maximum at T3 and T1, respectively. Additionally, a gradually decreased of ground diameter was observed with the decrease of light intensities. (2) Different responses of soil SOC content to shading were observed, the soil SOC content in T3 treatment was significantly lower than CK, while the opposite was observed in T4 treatment as compared with CK. Shading dcreased the content of TN in soil to varying degrees, but no significant difference among treatments were found. (3) The different responses of soil carbon and nitrogen metabolism enzymes to shading treatments were noticed. The soil enzyme activities were changed significantly under shading treatments as compared with CK, among which the soil cellulase (S-CL), soil sucrase (S-SC),soil acid invertase (S-AI) and soil lignin peroxidase (S-LiP) activities were highest at T4 treatment, soilcatalase(S-CAT), soilβ-N-acetylglucosaminidase(S-NAG) and soilchitinase(S-C) reached their maximum at T3 treatment, the soil polyphenol oxidase (S-PPO) activity was the highest at T1 treatment, and the soil amylase (S-AL), soil nitrite reductase (S-NiR) activity was the highest under T2. However, shading decreased the activities of soil urease (S-UE) and soil nitrate reductase (S-NR) to varying degrees. Redundancy analysis showed that soil enzyme activity explained 76.61% of SOC and TN, indicating S-LiP、S-AL、S-AI、S-PPO and S-CL had a strong positive correlation with SOC, while S-UE and S-NR had a great impact on TN. In summary, 30%-55% shading, namely light intensity between 542.68-856.31 μmol m^-2 s^-1 was suitable light condition for the growth of C. lanceolata seedlings, which is closely related with the improvement of soil carbon and nitrogen enzyme activity and ultimately the cycling of carbon and nitrogen nutrient under this circumstance.