Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland.
Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland.
Molecules. 2021 Apr 15;26(8):2283. doi: 10.3390/molecules26082283.
Compared to most other forest ecosystems, circumpolar boreal and subarctic forests have few tree species, and are prone to mass outbreaks of herbivorous insects. A short growing season with long days allows rapid plant growth, which will be stimulated by predicted warming of polar areas. Emissions of biogenic volatile organic compounds (BVOC) from soil and vegetation could be substantial on sunny and warm days and biotic stress may accelerate emission rates. In the atmosphere, BVOCs are involved in various gas-phase chemical reactions within and above forest canopies. Importantly, the oxidation of BVOCs leads to secondary organic aerosol (SOA) formation. SOA particles scatter and absorb solar radiation and grow to form cloud condensation nuclei (CCN) and participate in cloud formation. Through BVOC and moisture release and SOA formation and condensation processes, vegetation has the capacity to affect the abiotic environment at the ecosystem scale. Recent BVOC literature indicates that both temperature and herbivory have a major impact on BVOC emissions released by woody species. Boreal conifer forest is the largest terrestrial biome and could be one of the largest sources of biogenic mono- and sesquiterpene emissions due to the capacity of conifer trees to store terpene-rich resins in resin canals above and belowground. Elevated temperature promotes increased diffusion of BVOCs from resin stores. Moreover, insect damage can break resin canals in needles, bark, and xylem and cause distinctive bursts of BVOCs during outbreaks. In the subarctic, mountain birch forests have cyclic outbreaks of Geometrid moths. During outbreaks, trees are often completely defoliated leading to an absence of BVOC-emitting foliage. However, in the years following an outbreak there is extended shoot growth, a greater number of leaves, and greater density of glandular trichomes that store BVOCs. This can lead to a delayed chemical defense response resulting in the highest BVOC emission rates from subarctic forest in the 1-3 years after an insect outbreak. Climate change is expected to increase insect outbreaks at high latitudes due to warmer seasons and arrivals of invasive herbivore species. Increased BVOC emission will affect tropospheric ozone (O) formation and O induced oxidation of BVOCs. Herbivore-induced BVOC emissions from deciduous and coniferous trees are also likely to increase the formation rate of SOA and further growth of the particles in the atmosphere. Field experiments measuring the BVOC emission rates, SOA formation rate and particle concentrations within and above the herbivore attacked forest stands are still urgently needed.
与大多数其他森林生态系统相比，环极北方和亚北极森林的树种较少，容易发生食草昆虫的大规模爆发。长昼的短生长季节允许植物快速生长，而极地地区的预计变暖将刺激这种生长。土壤和植被中生物源挥发性有机化合物 (BVOC) 的排放可能在阳光明媚和温暖的日子里很大，生物胁迫可能会加速排放率。在大气中，BVOC 参与森林冠层内和上方的各种气相化学反应。重要的是，BVOC 的氧化导致次生有机气溶胶 (SOA) 的形成。SOA 颗粒散射并吸收太阳辐射，生长形成云凝结核 (CCN) 并参与云形成。通过 BVOC 和水分释放以及 SOA 形成和凝结过程，植被有能力在生态系统尺度上影响非生物环境。最近的 BVOC 文献表明，温度和食草动物都会对木质物种释放的 BVOC 排放产生重大影响。北方针叶林是最大的陆地生物群系之一，由于针叶树在地下和地上的树脂管中储存富含萜烯的树脂的能力，它可能是生物源单萜和倍半萜烯排放的最大来源之一。温度升高会促进树脂库中 BVOC 的扩散增加。此外，昆虫的损害会破坏针叶、树皮和木质部中的树脂管，并在爆发期间导致 BVOC 的显著爆发。在亚北极地区，山桦林周期性爆发尺蠖蛾。在爆发期间，树木通常会完全落叶，导致没有排放 BVOC 的叶子。然而，在爆发后的几年里，会有延长的新梢生长、更多的叶子和储存 BVOC 的腺毛密度更大。这可能导致化学防御反应延迟，从而导致昆虫爆发后 1-3 年内来自亚北极森林的最高 BVOC 排放率。由于季节变暖以及入侵食草动物物种的到来，预计气候变化将增加高纬度地区的昆虫爆发。增加的 BVOC 排放将影响对流层臭氧 (O) 的形成和 O 对 BVOC 的氧化。落叶树和针叶树引起的食草动物 BVOC 排放也可能增加 SOA 的形成速率，并进一步增加大气中的颗粒生长。在受食草动物攻击的林分中测量 BVOC 排放率、SOA 形成率和颗粒浓度的现场实验仍然非常紧迫。
