[Effects of different tree forms and grass mulching on microclimate in <i>Ziziphus jujuba</i> orchards in the plain regions of southern Xinjiang, China].

Tree form training and inter-row grass mulching are important components of modern orchard management. To explore optimal cultivation and management measures for mitigating the hazard effects of continuous high temperatures on dwarfed <i>Ziziphus jujuba</i> in the plain regions of southern Xinjiang, we conducted a split-plot experiment in a <i>Z. jujuba</i> orchard with three tree forms (open-center shape, OS; low spindle shape, LS; high spindle shape, HS) and two inter-row management practices (grass mulching, GR; clean cultivation control, CK). During a period of continuous high temperatures and irrigation suspension in August of the grass mulching year, we mea-sured air temperature and relative humidity at the upper, middle, and lower parts of the outer canopy (UC, MC, LC) at 10:00 and 16:00 every second day, as well as soil temperature and moisture at different soil depths (10 and 20 cm) under the canopy projection. Then, we analyzed the effects of tree form and inter-row management on microclimate factors. The results showed that: 1) tree form significantly influenced air temperature and soil tempe-rature. Air temperature of HS was reduced by 0.76 ℃ only at 10:00 compared with that of OS, while there was no significant change in LS compared with the other two tree forms. Soil temperature of HS was reduced by 0.98-1.75 ℃ and 0.95-1.29 ℃ compared with that of OS and LS, respectively. Soil temperature of LS was reduced by 0.17-0.46 ℃ compared with OS. 2) Grass mulching significantly influenced all microclimatic factors. Compared with CK, air and soil temperature of GR were reduced by 1.46-3.21 ℃ and 0.82-4.79 ℃, respectively, and the relative humidity of GR was increased by 24.1%-54.9%, but soil moisture of GR increased by 5.3% only at 10:00. 3) There were significant interactions between grass mulching and tree form to affect all microclimate factors, demonstrating strong cooling and humidifying effects. Grass mulching played a dominant role in regulating air temperature and relative humidity at the outer canopy of <i>Z. jujuba</i> trees, while tree form had a weaker adjustment effect. The microclimate indicators of both spindle shaped <i>Z. jujuba</i> trees exhibited higher sensitivity to grass mulching. The interaction between grass mulching and tree form played a prominent role in regulating soil temperature and moisture under canopy projection. In conclusion, inter-row grass mulching could serve as the primary practice for microclimate regulation of <i>Z. jujuba</i> trees, and its combination with spindle-shaped tree forms demonstrated beneficial effect in improving <i>Z. jujuba</i> treeś microclimate and mitigating the negative effects of high temperature in the plain region of southern Xinjiang.