FIGURE 6 Comprehensive
allelopathic effect index of Elymus nutans extracts on highland
grasses
4 DISCUSSION
Plant allelopathy is a traditional
subject and numerous studies have demonstrated that weeds can exhibit
allelopathic effects on economic crops (Nichols et al., 2015). Some
perennial grass, such as quackgrass (Agropyron repens ), ryegrass
(Lolium perenne ), red fescue (Festuca rubra ) and Kentucky
bluegrass have also been proved to be allelopathic to other plants
(Grummer 1961, Fales and Wakefield 1981). Recently, interest has
developed in the allelopathic on agroecosystems, like cultivated land
and commercial forest (Kural, 2020; Mushtaq, 2020). However, the role of
allelopathic effects of perennial grass on the seeds and seedlings of
crops and other grass species remain largely unknown. Our results
indicated that the extracts from drooping wildryegrass plant materials
and root zone soil did impact the germination and seedling growth of
commonly cultivated crops on plateau area and perennial grasses of
mix-seeded for vegetation restoration.
The effects of different extract treatments on germination varied with
crops and extract types. The annual monocots were more susceptible to
inhibition of the extracts, while the annual dicots tended to be more
tolerant or be promoted. The effects of drooping wildryegrass plant
materials and root zone soil extract on the growth of seedlings were
mainly manifested in inhibiting the growth of roots and shoots, and the
impact on monocot crops is greater than the impact on dicot crops. Out
results suggested that the three type extracts had no significant
inhibition or promotion on the seedlings growth of quinoa.
All tested grasses in this study were perennial, different from the
aforementioned crops. The highest germination force of control was
67.8% and the lowest was only 26.2%, reflecting the disuniformity of
germination. The germination rates of control of the five grasses ranged
from 63.8% to 81.8%. Except for Siberian wildryegrass which was
greater than 80%, the germination rate of other four species were all
less than 70%. The control germination index of the five grasses were
all less than 35%, reflecting the lower vitality of tested perennial
grass seeds.
Except that the root zone soil extract did not have a significant effect
on the two bluegrasses, other extract treatments caused significant
decrease in the germination force, germination rate and germination
index of the five grasses. The strongest inhibitory effect was the
pieces extract. Among the five grass species, the least affected was
Siberian wildryegrass, and the most affected was Chinese fescue, which
was consistent with previous reports (Liang et al., 2020). The effects
of the extracts on the growth of grass seedlings were mainly manifested
in the inhibition of the growth of roots, especially the growth of
drooping wildryegrass and Siberian wildryegrass. The three kinds of
extracts had no significant effect on the seedling growth ofKentucky bluegrass , but other extracts had inhibitive effects on
the growth of roots and shoots, as well as the dry weight. Particularly,
the effects of the pieces extract were more apparent. From allelopathic
perspective, these maybe reasonable explanations of the degradation of
mix-seeded pasture in alpine area.
Previous studies on autotoxicity of forage were mainly focused on
alfalfa and less reports of autotoxicity about Gramineae (Ghimire,
2019). The present study clearly demonstrated that drooping wildryegrass
had autotoxicity during its germination and seedling growth. This may
help to explain rapid decline of seed yield and above ground biomass of
drooping wildryegrass monoculture after 3 years.
The differences in the same index for the same crop and forage should be
attributed to different extracts. The composition of the whole plant
extract was analogous to that of rain leaching under natural conditions.
The plant pieces extract contained more components than whole plant
extract because sample ground destroyed the internal tissues of plants
and some enzymes, amino acids, inorganic salts, and nitrogen-containing
substances could solve in the extracts. The soil extract from the root
zone of drooping wildryegrass contained root exudates, leachate from
above-ground parts, as well as residues from the decomposition of dead
roots in the soil, and soil microorganisms related substances, although
the amount may be a little. The composition differences of extracts
might contribute to the indicator differences of the same crop or
forage.
5 CONCLUSIONS
Drooping wildryegrass
does have allelopathic potential
on germination and seedling growth of highland crops or perennial
grasses and the overall effect is inhibition. Different crops or
perennial grasses respond differently, and some are sensitive and some
are tolerant. The germination force (>80%) and germination
rate (>85%) of the control of five crops were relatively
higher, reflecting their good germination uniformity. Of the five crops,
hulless barley and oat are susceptible and quinoa is tolerant. Of the
five perennial grasses, Sibiricus wildryegrass is the least affected,
and Chinese fescue is the most affected. The responses of seed
germination and seedling growth of the same crop or grasses varies with
the extracts from different sources. The pieces extract has stronger
inhibition than others.
Drooping wildryegrass has less
allelopathic effects on Kentucky bluegrass and crymophylla bluegrass
than on Chinese fescue. It is recommended that the species combination
of mixture for restoration should consider allopathic effects of the
co-seeding and decrease the seeding rate of drooping wildryegrass in
mixture. The subsequent crop or grass followed seed production of
drooping wildryegrass monoculture should take planting annual dicots
into consideration.