不同种植方式下两种草本营养元素对土壤厚度和水分减少的响应

为了探究不同种植方式下草本植物对喀斯特"土层浅薄"和"岩溶干旱"生境的养分调节响应,选择苇状羊茅(Festuca arundinacea)和黑麦草(Lolium perenne)为研究材料,在盆栽水分控制条件下设置了2种土壤厚度对照土壤厚度(T_(CK))和浅土(T_S)]、2种水分处理对照水分(W_(CK))和干旱(W_D)]和2种种植方式(单种和混种),研究土壤厚度和水分减少对混种下两种草本植物元素含量、积累和分配的影响。结果表明:(1)与对照组(CK:T_(CK)W_(CK))相比,在浅土组(S:T_SW_(CK))、干旱组(D:T_(CK)W_D)和浅土+干旱组(SD:T_SW_D),苇状羊茅和黑麦草的地上和根系C和N含量在单种和混种下(浅土除外)显著增加,P含量和各部分元素积累量显著降低;而苇状羊茅的根系各元素分配比在3种低资源水平下(S、D、SD)由单种时增加转为混种时降低,而黑麦草的根系营养元素分配比在浅土中增加,但在干旱处理下减少。(2)在对照资源水平下(CK),混种后苇状羊茅的地上部分C含量、根系P含量、地上、地下和总的元素积累量和根系元素分配比显著高于单种,而在3种低资源水平下达到各参数在单种和混种下无显著差异。(3)在各资源水平下,混种后黑麦草各部分C、N、P的含量、积累量和根系元素分配比大体上与单种无显著差异。结果表明,在低资源水平下,苇状羊茅和黑麦草通过增加C和N元素含量表现出较强的资源获取和防御能力。在混种条件下,苇状羊茅能够通过调节自身元素的积累和分配来提高竞争力,而黑麦草保持相对恒定的策略来响应竞争。

Responses of nutrient elements of two grasses to the decline of soil thickness and/or water under different planting patterns

The karst ecosystems in southwest China are extremely fragile and vulnerable. The phenomenon of rocky desertification has become more serious, which causes karst soil to be scarcer and shallower. In addition, under the change of global rainfall pattern, the climate in SW China appears to have the trend of high temperature, low rainfall, and frequent occurrence of the continuous extreme drought events, which exacerbates the frequency and intensity of karst drought. Plants in karst regions have strong morphological plasticity and physiological regulation ability to minimize the impact of adverse environmental factors, such as shallow soil and drought. Meanwhile, in order to maximize the use of limited resources, plants in karst regions may have some ecological niche differentiation to reduce the inhibition of resource limitation on co-existence species. The nutritional characteristics play an important role in plant growth and physiological regulation, and might reveal clues about the adaptive and competitive mechanisms of plants in karst habit with shallow soil and karst drought. The gramineous perennial grass, Festuca arundinacea, is a deep-rooted plant as the root can be up to 40 cm depth in soil, while Lolium perenne, with root depth up to 25 cm, is a shallow-rooted plant. These two species are both introduced as pioneer grasses for re-vegetation in karst regions due to their high drought resistance, barren-tolerance, strong ecological adaptability, high yield and good economic benefit. They effectively improve the local ecological environment and help to alleviate rural poverty. Therefore, we chose these two species to study the effects of decline of soil thickness and/or water on the nutrient element contents, accumulation and distribution under different planting patterns. In our study, three factors, namely soil thickness (T_CK:15 cm, and T_S:5 cm), water (W_CK:120 mL/3 d and W_D:36 mL/3 d), and planting pattern (monoculture and mixture) were designed in a full three-way randomized block design. The results showed that:(1) Compared with control group (CK:T_CKW_CK), the C and N contents in aboveground part, root, and whole plant of both species increased (except in shallow soil group, S:T_SW_CK), while the P contents and their accumulations decreased in the shallow soil group (S:T_SW_CK), drought group (D:T_CKW_D), and shallow soil plus drought group (SD:T_SW_D) both in monoculture and in mixture. The root nutrient distribution ratio of F. arundinacea increased in monoculture but decreased in mixture at three low resource levels (S, D, SD). The root nutrient distribution ratio of L. perenne increased in the shallow soil group, but decreased in the drought group. (2) The C content in aboveground part, P content in root, and their accumulations of each part and root nutrient distribution ratio of F. arundinacea were significantly higher in mixture than in monoculture at control resource level (CK), while there was no-significant difference between mixture and monoculture for above traits of F. arundinacea at low resources levels. (3) At all resource levels, there was no significant difference between monoculture and mixture for all the above traits of L. perenne. The results indicated that both species had higher absorbing-resource and defense abilities by increasing C and N contents at low resource levels. In mixed planting, F. arundinacea could improve its competitiveness by adjusting element accumulation and distribution, while L. perenne might maintain a constant strategy of nutrient regulation in response to competition.