Allelopathic Effects Of Decomposed Leaf Litters Of Forests On Shrubs And Grasses Under Tree Layers In The Loess Plateau

Compared with the artificial forests, forest and grass complex ecosystem hasobvious advantages in stability, resisting pests and diseases, utilization of solar energy, easethe contradiction of forestry and husbandry and developing economic benefits, social benefitsand ecological benefits. However, whether there exist allelopathic effects between plantationspecies and some shrubs and grasses, especially whether decomposed leaf litters of trees haveinhibition allelopathic effects on seed germination and seedling growth of shrubs and grassesis not clear.Based on extensive investigations of common forest and grass complex type in theLoess Plateau, we selected13kinds of common plantation species (4kinds of coniferoustrees,6kinds of broad-leaved trees, and3kinds of broad-leaved shrubs) as research objects,mixed them with soil separately and incubated in laboratory, then we obtained differentconcentrations (10,20and40mg mL-1) of water extracts from decomposed leaf litters asculture medium, and studied their allelopathic effects on Medicago sativa, Vicia villosa,Melilotus officinalis and Amorpha fruticosa seed germination, seedling growth andphysiological activities, and then we studied whether these decomposed leaf litters haveallelopathic effects on shrubs and grasses, and its strength. Main results as follows:(1) On Medicago sativa, Platycladus orientalis, Salix matsudana and Betulaplatyphylla showed significant stimulation, while Ulmus pumila, Quercus liaotungensis andAmorpha fruticosa showed significant inhibition, at the same time, the stimulating effects ofSalix matsudana and Betula platyphylla decreased as the concentration of extracts increased;Pinus tabulaeformis, Pinus sylvestris var. Mongolica, Larix principis-rupprechtii, Populussimonii, Robinia pseudoacacia, Caragana microphylla and Hippophae rhamnoides showedthe law of "lower-stimulation and higher-inhibition", therefore, when we selected trees thatplanted together with Medicago sativa, Platycladus orientalis, Salix matsudana and Betulaplatyphylla were the preferred species, Ulmus pumila, Quercus liaotungensis and Amorphafruticosa should be used sparingly or not, if Pinus tabulaeformis, Pinus sylvestris var.Mongolica, Larix principis-rupprechtii, Populus simonii, Robinia pseudoacacia, Caragana microphylla and Hippophae rhamnoides were used, intercropping density should be givenfull consideration, and leaf litters would be cleared appropriately.(2) On Vicia villosa, Ulmus pumila, Salix matsudana and Betula platyphyllashowed significant stimulation, while Pinus tabulaeformis, Robinia pseudoacacia,Hippophae rhamnoidesandAmorpha fruticosa showed significant inhibition, Pinus sylvestrisvar. Mongolica, Larix principis-rupprechtii, Platycladus orientalis, Quercus liaotungensis,Populus simonii and Caragana microphylla showed the law of "lower-stimulation andhigh-inhibition", therefore, when we selected trees that planted together with Vicia villosa，Ulmus pumila, Salix matsudana and Betula platyphylla were the preferred species, Pinustabulaeformis, Robinia pseudoacacia, Hippophae rhamnoides and Amorpha fruticosa shouldbe used sparingly or not, if Pinus sylvestris var. Mongolica, Larix principis-rupprechtii,Platycladus orientalis，Quercus liaotungensis，Populus simonii and Caragana microphyllawere used, intercropping density should be given full consideration, and leaf litters would becleared appropriately.(3) On Melilotus officinalis，Quercus liaotungensis showed significant stimulation,while Salix matsudana showed significant inhibition, the inhibition effects of Salixmatsudana increased with the concentration of extracts increased; Pinus tabulaeformis, Pinussylvestris var. Mongolica, Larix principis-rupprechtii, Platycladus orientalis, Populus simonii,Ulmus pumila, Robinia pseudoacacia, Betula platyphylla, Caragana microphylla, Hippophaerhamnoides and Amorpha fruticosa(at low concentration) showed stimulation, stimulationeffects decreased, disappeared and even showed certain inhibition at middle concentration, athigh concentration, these trees all showed inhibition, of which Populus simonii, Ulmuspumila and Robinia pseudoacacia were greater inhibition strength trees. when we selectedtrees that planted together with Melilotus officinalis, Quercus liaotungensis was the preferredspecies, followed by Larix principis-rupprechtii, Betula platyphylla and Amorpha fruticosa,Populus simonii, Ulmus pumila and Robinia pseudoacacia should be used with caution, Salixmatsudana should be used sparingly or not, if Pinus tabulaeformis, Pinus sylvestris var.Mongolica, Platycladus orientalis, Caragana microphylla and Hippophae rhamnoides wereused to planted with Melilotus officinalis, planting density should be controlled reasonably,and leaf litters would be cleared appropriately.(4) On Amorpha fruticosa, Ulmus pumila showed significant stimulation, whileLarix principis-rupprechtii and Quercus liaotungensis showed significant inhibition, Pinustabulaeformis, Pinus sylvestris var. Mongolica, Platycladus orientalis, Populus simonii,Robinia pseudoacacia, Salix matsudana and Betula platyphylla(at low concentration) allshowed stimulation, at middle concentration, the stimulation effects decreased(Pinus sylvestris var. Mongolica, Populus simonii and Salix matsudana), disappeared(Robiniapseudoacacia and Betula platyphylla), and even showed inhibition(Pinus tabulaeformis andPlatycladus orientalis), at high concentration, these trees all showed inhibition, of whichPinus tabulaeformis, Pinus sylvestris var. Mongolica, Platycladus orientalis and Betulaplatyphylla were greater inhibition strength trees. when we selected trees that planted togetherwith Amorpha fruticosa, Ulmus pumila was the preferred species, followed by Pinussylvestris var. Mongolica, Populus simonii, Salix matsudana and Pinus tabulaeformis, Larixprincipis-rupprechtii and Quercus liaotungensis should be used sparingly or not, ifPlatycladus orientalis， Robinia pseudoacacia and Betula platyphylla were used, plantingform and planting density should be controlled reasonably, and leaf litters would be clearedappropriately.