School of Forest Resources and Conservation, University of Florida, Gainesville, FL, USA.
Department of Plant Pathology, University of Florida, Gainesville, FL, USA.
Mol Ecol. 2019 Nov;28(22):4971-4986. doi: 10.1111/mec.15263. Epub 2019 Nov 6.
A prevailing paradigm in forest ecology is that wood-boring beetles facilitate wood decay and carbon cycling, but empirical tests have yielded mixed results. We experimentally determined the effects of wood borers on fungal community assembly and wood decay within pine trunks in the southeastern United States. Pine trunks were made either beetle-accessible or inaccessible. Fungal communities were compared using culturing and high-throughput amplicon sequencing (HTAS) of DNA and RNA. Prior to beetle infestation, living pines had diverse fungal endophyte communities. Endophytes were displaced by beetle-associated fungi in beetle-accessible trees, whereas some endophytes persisted as saprotrophs in beetle-excluded trees. Beetles increased fungal diversity several fold. Over forty taxa of Ascomycota were significantly associated with beetles, but beetles were not consistently associated with any known wood-decaying fungi. Instead, increasing ambrosia beetle infestations caused reduced decay, consistent with previous in vitro experiments that showed beetle-associated fungi reduce decay rates by competing with decay fungi. No effect of bark-inhabiting beetles on decay was detected. Platypodines carried significantly more fungal taxa than scolytines. Molecular results were validated by synthetic and biological mock communities and were consistent across methodologies. RNA sequencing confirmed that beetle-associated fungi were biologically active in the wood. Metabarcode sequencing of the LSU/28S marker recovered important fungal symbionts that were missed by ITS2, though community-level effects were similar between markers. In contrast to the current paradigm, our results indicate ambrosia beetles introduce diverse fungal communities that do not extensively decay wood, but instead reduce decay rates by competing with wood decay fungi.
森林生态学中的一个主流观点认为，蛀木甲虫促进了木材腐朽和碳循环，但实证研究的结果却喜忧参半。本研究在美国东南部通过实验确定了蛀木甲虫对松树干内真菌群落组成和木材腐朽的影响。松树干设置为可供甲虫进入或不可供甲虫进入两种情况。通过培养和高通量扩增子测序（HTAS）对 DNA 和 RNA 进行真菌群落比较。在甲虫侵袭之前，活体松树具有多样化的真菌内生菌群落。在可进入甲虫的树木中，甲虫相关真菌取代了内生真菌，而在被甲虫排斥的树木中，一些内生真菌则作为腐生菌存活下来。甲虫使真菌多样性增加了数倍。有超过 40 个子囊菌门的分类群与甲虫显著相关，但甲虫并不总是与任何已知的木材腐朽真菌相关。相反，随着粉蠹虫侵染的增加，腐朽减少，这与先前的体外实验结果一致，即甲虫相关真菌通过与腐朽真菌竞争而降低腐朽速率。未检测到树皮栖息甲虫对腐朽的影响。扁甲科携带的真菌分类群明显多于小蠹科。分子结果通过人工合成和生物模拟群落进行了验证，并与不同方法一致。RNA 测序证实了甲虫相关真菌在木材中具有生物活性。LSU/28S 标记的 metabarcoding 测序回收了重要的真菌共生体，这些共生体被 ITS2 忽略，但两种标记的群落水平效应相似。与当前的范式相反，我们的结果表明，粉蠹虫引入了多样化的真菌群落，这些真菌群落不会广泛地腐朽木材，而是通过与木材腐朽真菌竞争来降低腐朽速率。
