Study On Moisture And Light Utilization Characteristics And Regulation Mechanism Of Sod-culture Apple Orchard In Cool Area

Coordinating the relationship between the fruit trees and the environment is the important pathway to the sustainable development of fruit industry. Therefore, keeping the high quality of soil, as the important medium for the sustainable development of fruit industry, is essential. Bare earth, the traditional soil management system, severely broke the biological processes in topsoil. It also decreased the content of soil organic matter and stability of the microbial community structure, and then resulting in soil nutrient imbalances and environmental degradation which has become one of the major bottlenecks to the sustainable development of fruit industry. Considering the important function of maintaining soil fertility and improving soil environment, orchard grassing has become one of the key technologies of safe and high-quality continuous fruit production. Photosynthesis is the basis of the fruit yield. Moisture and light are not only the important environmental factors affecting photosynthesis, but also the most sensitive environmental factors of the coexistent system between fruit and grass.’Hanfu’ apple orchard, with grass coverage in cool region, was used to study the effect of grass coverage on moisture and light utilization characteristics of’Hanfu’ apple, and physiological and ecological mechanism of interactions between trees and grass under shading and pruning (or mowing) conditions. Major factors affecting water and solar energy utilization of ’Hanfu’ apple tree under grassing condition are discussed. The main results are as follows:1.ψo,φEo, RC/CSo, ETo/CSo, PIcs and ΔI were elevated with the enhanced photosynthetic capacity under grass coverage and bare earth conditions. RC/CSo, ETo/CSo, PICS and ΔI in young leaf were significantly higher than that in mature leaf under the two conditions. The function of PSII in young leaf have developed to a great extent. In May7, Fv/Fm, PIcs and ΔI under grass coverage condition were significant higher than that under bare earth. Development of PSII and PSI function under grass coverage were earlier than that under bare earth and therefore had a higher photosynthetic efficiency.2. Compared to bare earth condition, AQY and Pm of ’Hanfu’ apple leaf in natural high-temperature and high-light were significantly higher under grass coverage condition. The energy flux (per reaction centre) for absorption (ABS/RC) and dissipation (DIo/RC) significantly decreased. The maximal quantum yield of primary photochemistry (Fv/Fm) and and the efficiency (ψo) significantly increased which lead to the significant increase of performance index (PIabs). Therefore, grass coverage is able to coordinate the relationship between the PSI and PSII, improved the activity of PSI and PSII and relieved the photoinhibition to photosynthetic apparatus in high-temperature and high-light.3. Compared to bare earth condition, the activity of SOD and POD in’Hanfu’ apple leaf increased by an average of12.7%and11.4%, respectively, during leaf ageing under grass coverage. At the same time, the content of O2-and H2O2decreased by an average of21.2%and2.8%, respectively, which reduced or delayed the occurrence of membrane lipid peroxidation and mitigated the damage to function and structure of chloroplast. Fv/F0and Fm under grass coverage were significantly higher than that under bare earth at mid-late and late stage. Pn under grass coverage condition was significantly higher than that under bare earth at early-middle, middle and late-middle stage of leaf ageing. The results indicated that grass coverage, to a certain extent, could reduce or delay the damage of senescence on structure and function of PSⅡ. It also improved the leaf ability of manufacturing the assimilates,4. From May to October, the soil water content (SWC) of10cm layer in alley grassing area in June, July, September and October were significantly higher than that in alley bare earth area, and SWC of20cm layer were significantly higher than that in alley bare earth from June to September. However, SWC of30cm layer were significantly higher than that in alley bare earth only in June, and SWC of40cm layer were significantly higher from August to October. It can be speculated that0-30cm topsoil was the main root distribution area of grass. SWC of10cm layer in June, and60cm layer from June to October in grass mulch area were significantly higher than that in bare earth area inline, while SWC of20cm layer from May to September,30cm alyer from May to August, and40cm layer in July and September significantly lower than that in bare earth area inliine. It can be inferred that0-40cm topsoil was the main apple root distribution area in grass mulch area, and the distribution of apple root were deeper in bare earth area than that in grass mulch area. The results suggested that the0-40cm topsoil was the main area, where existed the interaction for water between apple trees and grass.5. Mowing for20cm of red clover stubble increased photosynthetic efficiency, prolong the effective photosynthetic time and increased branching number. In addition, the degree of fibrosis and the number of tillers of red clover were in the middle compared with the other treatments. Mowing for20cm stubble were beneficial to establishing the continuous production of grass group and improvement of total output. Therefore, mowing for20cm stubble was the suitable height for the planted red clover group.6. Compared to the ’grass mulch’(GM) treatment, Soil temperature in’grass mulch+shade’(GM+S) treatment was too low and increased slowly, while the air temperature rose rapidly at10:00in summer.’GM+S’also accelerated the accumulation of QA-in acceptor side of PSⅡ and the significantly reduction of maximum quantum yield of primary photochemistry and quantum yield for electron transport. Soil temperature in ’bare earth’ treatment (CK) was the highest among the three treatments and increased rapidly. The quantum yield for electron transport of apple leaf significantly decreased than that in GM due to the accumulation of QA-in acceptor side of PSII. The Pn of apple leaf were descending order in GM,’GM+S’and CK treatments, and the Pn was significant difference between GM and CK treatments. Therefore, the thickness of grass mulch shouldn’t be too thick in grass coverage orchard. However,’GM+S’and’GM’ treatments delay the period of the photosynthetic efficiency decline under drought and water saturation stress conditions, and promoted the recovery of the photosynthetic efficiency under rewatering after drought stress.7. The Pn of apple leaf, at the4d after drought, were decreased into the29.0%,9.3%and1.4%of the Pn at the1d after drought in red clover, bluegrass and bare earth treatments, respectively, and PIabs were decreased into the68.6%,60.3%and28.5%of the PIabs at the1d after drought, respectively. This indicated the adaptability of apple trees to drought stress were improved by red clover and bluegrass treatments compared with the bare earth, while the adaptability in red clover treatment was better than that in bluegrass. At the3d after rewatering, Pn of apple leaf were recovered into the81.3%、80.1%and64.1%of the Pn at the1d after drought in red clover, bluegrass and clean tillage treatments, respectively. The results indicated that red clover and bluegrass treatments availed to the recovery of apple leaf photosynthetic efficiency in rewatering period, and the effect of red clover was better than that of bluegrass. White clover treatment alleviated the damage to oxygen evolving complex and the acceptor side of PSII, increased the maximum quantum yield of primary photochemistry and quantum yield for electron transport of PSII and maintained the higher performance of PSII during the flooding process. Finally, white clover treatment maintained the higher photosynthetic efficiency of apple leaf. The effect of bluegrass was opposite to the white clover.