Widespread autotoxicity is an important obstacle to natural regeneration of many plants. The rare relict plant Metasequoia glyptostroboides is a difficult to natural regeneration and is affected by litter allelopathy. However, little is known about the potential influence of autotoxic substances on different regeneration stages of M. glyptostroboides. We identified multiple chemical compounds of aqueous extracts from fresh (recently accumulated) and natural litter (mixture of litter different phases of decomposition), to evaluate the autotoxic effects of the four most important detected compounds applied individually on seed germination and seedling growth of M. glyptostroboides. Results found that the 28 chemical compounds were identified in the aqueous extracts of M. glyptostroboides litter. The Jaccard similarity coefficient of chemical compounds in aqueous extracts of fresh and natural litter of M. glyptostroboides reached 50%. The number of chemical compounds in fresh litter was 5.56% more than that in natural litter. Catechol, trifluoroacetamide, benzoic acid and D-(+)-arabitol significantly affected seed germination rate, seed germination index, vigor index, shoot length and main root length of M. glyptostroboides. Specifically, benzoic acid had the strongest inhibitory effect, followed by catechol, trifluoroacetamide and D-(+)-arabitol. The autotoxic effect was concentration dependent, low concentrations were positive and neutral, high and extremely high concentrations were negative for all the chemical compounds. Moreover, catechol, trifluoroacetamide, benzoic acid and D-(+)-arabitol were autotoxic substances affecting the natural regeneration of M. glyptostroboides, as well as strongly inhibited at the shoot growth stage. This study confirms that natural regeneration of M. glyptostroboides is restricted by a large amount of litter coverage under the forest, highlighting how the chemical compounds responsible for the autotoxic characteristics of M. glyptostroboides affect the different regeneration stages of M. glyptostroboides.

Stem cracks are becoming a major problem affecting timber quality and its economic value; their frequency may increase with increasing frequency and severity of drought stress due to climate change. Several major conifer species are affected, but such damage was mentioned for the first time in France for hybrid larch (Larix x eurolepis) in 1993. Even though a link was made with severe drought some years ago, it was believed, at that time, that the rapid growth of hybrids might be the cause. Our study is intended to disentangle the role of growth versus drought in the appearance of cracks, based on observations in two field genetic trials. Summer drought was clearly identified as the main trigger of longitudinal cracks. Roughly 5–15 years of age seems to be the critical period during which the occurrence of most of the cracks was observed. Wood formed during this period corresponds to juvenile wood, well-known for its weaknesses. Nevertheless, some trees escaped cracking damage: compared to trees with cracks, these looked slender (higher HD ratio), had wider rings and greater grain angle in the early years but similar wood density. Fast growth has often been cited as enhancing crack occurrence. This conclusion is corroborated by our observations that, within a given variety or family, trees with cracks were consistently larger than trees without cracks. Nevertheless, this conclusion should be qualified by the additional observation that, across varieties/families, the faster growing material were not necessarily the most prone to cracks, highlighting the crucial role of the genetic background of the material planted.