Mosca E, Montecchio L, Barion G, Dal Cortivo C, Vamerali T
Faculty of Science and Technology, Free University of Bolzano, Piazza Università 1, 39100 Bolzano, Italy.
Research and Innovation Centre, Edmund Mach Foundation, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy.
Ann Bot. 2017 May 1;119(7):1235-1246. doi: 10.1093/aob/mcx007.
Oak decline is a complex phenomenon, characterized by symptoms of canopy transparency, bark cracks and root biomass reduction. Root health status is one of the first stress indicators, and root turnover is a key process in plant adaptation to unfavourable conditions. In this study, the combined effects of decline and thinning were evaluated on fine root dynamics in an oak forest adjoining the Italian Pre-Alps by comparison of acute declining trees with non-declining trees, both with and without thinning treatment of surrounding trees.
Dynamics of volumetric root length density (RLD V ) and tip density (RTD V ), root tip density per unit length of root (RTD L ), diameter, branching index (BI) and mycorrhizal colonization were monitored by soil coring over 2 years as possible descriptors of decline.
At the beginning of the experiment, the relationship between canopy transparency and root status was weak, declining trees having slightly lower RLD V (-20 %) and RTD V (-11 %). After a 1 year lag, during which the parameters were almost unaffected, BI and RLD V , together with tip density, tip vitality and mycorrhizal colonization, became the descriptors most representative of both decline class and thinning. Thinning of declining trees increased RLD V (+12 %) and RTD V (+32 %), but reduced tip mycorrhizal colonization and vitality over time compared with non-thinned trees, whereas the opposite occurred in healthy trees, together with a marked decrease in branching. After thinning, there was an initial reduction in the structure of the ectomycorrhizal community, although recovery occurred about 10 months later, regardless of decline severity.
Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by oak roots. The close correlation between root vitality and mycorrhizal colonization and their deterioration after thinning indicates that decline does not benefit from reduced root competition, excluding the hypothesis of limited water and nutrient availability as a possible cause of the syndrome in this forest.
橡树衰退是一种复杂的现象，其特征为树冠透光、树皮开裂和根系生物量减少。根系健康状况是最早的胁迫指标之一，而根系周转是植物适应不利条件的关键过程。在本研究中，通过比较急性衰退树木与未衰退树木（周围树木均有或无疏伐处理），评估了衰退和疏伐对意大利前阿尔卑斯山附近橡树林细根动态的综合影响。
通过土壤取芯，在两年时间内监测体积根长密度（RLD V）、根尖密度（RTD V）、单位根长根尖密度（RTD L）、直径、分支指数（BI）和菌根定殖情况，将其作为衰退的可能描述指标。
在实验开始时，树冠透光与根系状况之间的关系较弱，衰退树木的RLD V（-20%）和RTD V（-11%）略低。经过1年的滞后，在此期间参数几乎未受影响，BI和RLD V以及根尖密度、根尖活力和菌根定殖成为最能代表衰退等级和疏伐情况的描述指标。与未疏伐的树木相比，对衰退树木进行疏伐增加了RLD V（+12%）和RTD V（+32%），但随着时间推移降低了根尖菌根定殖和活力，而在健康树木中情况则相反，同时分支显著减少。疏伐后，外生菌根群落结构最初有所减少，尽管约10个月后出现恢复，且与衰退严重程度无关。
衰退导致细根长度损失，疏伐可实现适度恢复，使橡树根系能更好地探索土壤。根系活力与菌根定殖之间的密切关联以及疏伐后它们的恶化表明，衰退并未因根系竞争减少而受益，排除了水分和养分供应有限作为该森林中该综合征可能原因的假设。
