ABSTRACT Frost damage is the most important abiotic risk in Acacia mearnsii (black wattle) plantations in South Africa. Current A. mearnsii planting stock cannot tolerate temperatures below −4°C, and therefore there is an urgent need to develop frost-tolerant seed. This study investigated the frost hardiness of seedlots from six South African A. mearnsii seed orchards located at altitudes of 1120–1458 m asl and latitudes of 26.7–29.8°S that were established with cold-hardy Australian provenances and/or local landraces from cold sites. Frost damage was assessed in four field trials established on two different dates in 2015. Three sites experienced extensive frost events, with frequency and intensity varying among sites. Minimum temperatures ranged from −6.4°C to −7.7°C across sites. The seedlot from the coldest, highest altitude orchard showed superior frost hardiness to other seedlots from lower altitude and warmer orchards of similar genetic origin. Thus, site climatic characteristics are important for the development of cold hardiness in A. mearnsii seed orchards. Frost hardiness in young A. mearnsii trees was significantly related to age and tree size. At four months of age, trees were highly susceptible to frost damage irrespective of tree size and orchard origin (60–71% frosted trees). Frost hardiness increased with age and was very high at c. nine months across orchards (1–8% frosted trees at one site and 0–2% at another site). At nine months, although the extent of frost damage was low, this was inversely related to tree size. The percentage of trees that recovered from frost damage also increased with age of frost damage, this being 21% at the site frosted at four months of age and 65–67% at the sites frosted at nine months of age. Finally, there were no differences in tree growth at 14 months suggesting that, unlike cold hardiness, the differences in environment between the orchards did not affect the growth performance of the offspring.

中文翻译：

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六种金合欢（黑荆）种子园的抗冻性及发育阶段和树体大小对抗冻性的影响

摘要 霜害是南非金合欢（黑荆）种植园最重要的非生物风险。目前的 A. mearnsii 种苗不能耐受低于 -4°C 的温度，因此迫切需要开发抗冻种子。本研究调查了位于海拔 1120-1458 m 和纬度 26.7-29.8°S 的六个南非 A. mearnsii 种子园的种子园的抗寒性，这些种子园是用耐寒的澳大利亚原产地和/或来自寒冷的当地地方品种建立的。网站。霜冻损害在 2015 年两个不同日期建立的四项现场试验中进行了评估。三个地点经历了广泛的霜冻事件，地点之间的频率和强度各不相同。各站点的最低温度范围为 -6.4°C 至 -7.7°C。最冷的苗圃，海拔最高的果园显示出比来自低海拔和温暖的类似遗传起源的果园的其他苗圃更好的抗冻性。因此，场地气候特征对于 A. mearnsii 种子园的耐寒性发展很重要。年轻的 A. mearnsii 树木的抗寒性与年龄和树木大小显着相关。在四个月大的时候，无论树木大小和果园起源如何（60-71% 的树有霜冻），树木都非常容易受到霜冻伤害。抗冻性随着年龄的增长而增加，并且在 c 时非常高。整个果园 9 个月（一个地点 1-8% 的树木结霜，另一地点 0-2% 的树木）。在 9 个月时，虽然冻害程度较低，但这与树木大小成反比。从冻害中恢复的树木的百分比也随着冻害年龄的增加而增加，这在四个月龄结霜的地点为 21%，在九个月龄结霜的地点为 65-67%。最后，14 个月时树木生长没有差异，这表明与抗寒性不同，果园之间的环境差异不会影响后代的生长性能。